Happened to me too just yesterday. Core crashed and I booted it back up and had a corrupted database, so I told it to rebuild and it crashed again. Then it wouldn't get past the loading screen without crashing, so I deleted everything in my \Bitcoin\ directory and reinstalled Core 0.12 and the same thing kept happening, crash at the loading screen. I tried installing my \Bitcoin\ directory on another physical drive and still same thing happened. After deleting and reinstalling about 5 times it finally booted up and started syncing again. I think this is my computer telling me it's too old for this sh.t any more.
So v0.12 is a total bust for me. It crashed once more and I cannot get it to start up no matter what. It sometimes makes it to "checking addresses" on the loading screen, but never any further. Sometimes it crashes as soon as the loading screen appears. I went back to 0.11.2 and it loads just find so it is a bug specific to 0.12.
Here are a few of my logs from the crashes, you can see the program just stops with no indication of any sort of error.
2016-02-26 15:14:47 Bitcoin version v0.12.0 (2016-02-17 09:40:03 +0100)
2016-02-26 15:14:47 InitParameterInteraction: parameter interaction: -whitelistforcerelay=1 -> setting -whitelistrelay=1
2016-02-26 15:14:47 GUI: registerShutdownBlockReason: GetProcAddress for ShutdownBlockReasonCreate failed
2016-02-26 15:14:48 Using OpenSSL version OpenSSL 1.0.1k 8 Jan 2015
2016-02-26 15:14:48 Using BerkeleyDB version Berkeley DB 4.8.30: (April 9, 2010)
2016-02-26 15:14:48 Default data directory [editted out]
2016-02-26 15:14:48 Using data directory [editted out]
2016-02-26 15:14:48 Using config file [editted out]
2016-02-26 15:14:48 Using at most 125 connections (2048 file descriptors available)
2016-02-26 15:14:48 Using 2 threads for script verification
2016-02-26 15:14:48 Using wallet wallet.dat
2016-02-26 15:14:48 scheduler thread start
2016-02-26 15:14:48 init message: Verifying wallet...
2016-02-26 15:14:48 CDBEnv::Open: LogDir=[editted out] ErrorFile=[editted out]
2016-02-26 15:14:48 Error: Couldn't open socket for incoming connections (socket returned error An address incompatible with the requested protocol was used. (10047))
2016-02-26 15:14:48 Bound to 0.0.0.0:8333
2016-02-26 15:14:48 Cache configuration:
2016-02-26 15:14:48 * Using 2.0MiB for block index database
2016-02-26 15:14:48 * Using 32.5MiB for chain state database
2016-02-26 15:14:48 * Using 65.5MiB for in-memory UTXO set
2016-02-26 15:14:48 init message: Loading block index...
2016-02-26 15:14:48 Opening LevelDB in [editted out]
2016-02-26 15:14:48 Opened LevelDB successfully
2016-02-26 15:14:48 Using obfuscation key for [editted out]: 0000000000000000
2016-02-26 15:14:48 Opening LevelDB in [editted out]
2016-02-26 15:14:48 Opened LevelDB successfully
2016-02-26 15:14:48 Using obfuscation key for [editted out]: 72046a1e7622fad5
2016-02-26 15:14:57 LoadBlockIndexDB: last block file = 197
2016-02-26 15:14:57 LoadBlockIndexDB: last block file info: CBlockFileInfo(blocks=365, size=131274522, heights=330521...330993, time=2014-11-18...2014-11-21)
2016-02-26 15:14:57 Checking all blk files are present...
2016-02-26 15:14:58 LoadBlockIndexDB: transaction index disabled
2016-02-26 15:14:58 LoadBlockIndexDB: hashBestChain=00000000000000001639f0ef7eb082b57e48f33baeb9082a7ab07ef3ef7df130 height=330922 date=2014-11-21 00:37:07 progress=0.450084
2016-02-26 15:14:58 init message: Verifying blocks...
2016-02-26 15:14:58 Verifying last 288 blocks at level 3
2016-02-26 15:15:14 No coin database inconsistencies in last 36 blocks (26535 transactions)
2016-02-26 15:15:14 block index 26188ms
2016-02-26 15:15:14 init message: Loading wallet...
2016-02-26 15:15:15 nFileVersion = 120000
2016-02-26 15:15:15 Keys: 0 plaintext, 265 encrypted, 265 w/ metadata, 265 total
2016-02-26 15:15:15 wallet 281ms
2016-02-26 15:15:15 init message: Activating best chain...
2016-02-26 15:15:16 UpdateTip: new best=000000000000000012e7c144fc1c1038c2e7826033b8c9739e5e690b8bf40b91 height=330923 log2_work=81.519843 tx=51953838 date=2014-11-21 00:49:03 progress=0.450093 cache=0.4MiB(1228tx)
2016-02-26 15:15:19 UpdateTip: new best=00000000000000001acb1484131a0b69c7666e1a9b94e483babae59adf1fe160 height=330924 log2_work=81.519915 tx=51954895 date=2014-11-21 01:02:32 progress=0.450110 cache=15.2MiB(4216tx)
2016-02-26 15:15:22 UpdateTip: new best=000000000000000005357156756d6576017e084a6ad8505fd2721feb79773b6c height=330925 log2_work=81.519987 tx=51956910 date=2014-11-21 01:56:55 progress=0.450152 cache=17.7MiB(8185tx)
2016-02-26 15:15:24 UpdateTip: new best=00000000000000001062194213863dab2ef62cb1f7715329927c6d24dc0dc0fd height=330926 log2_work=81.520059 tx=51957644 date=2014-11-21 01:57:29 progress=0.450160 cache=21.0MiB(9680tx)
2016-02-26 15:15:26 UpdateTip: new best=00000000000000000a99e0837981a3ffb45b20b14a4f30e6be51eb014a69a850 height=330927 log2_work=81.520131 tx=51959086 date=2014-11-21 02:14:09 progress=0.450182 cache=22.4MiB(11784tx)
2016-02-26 15:15:29 UpdateTip: new best=0000000000000000178e4ae780a4e48f28c1cf6e061167b92e3ee1f75e166a37 height=330928 log2_work=81.520203 tx=51960689 date=2014-11-21 02:40:51 progress=0.450210 cache=25.6MiB(14222tx)
2016-02-26 15:15:29 mapBlockIndex.size() = 400090
2016-02-26 15:15:29 nBestHeight = 330928
2016-02-26 15:15:29 setKeyPool.size() = 98
2016-02-26 15:15:29 mapWallet.size() = 307
2016-02-26 15:15:29 mapAddressBook.size() = 64
2016-02-26 15:15:29 init message: Loading addresses...
2016-02-26 15:15:29 torcontrol thread start
2016-02-26 15:15:29 ERROR: Read: Failed to open file [editted out]
2016-02-26 15:15:29 Invalid or missing banlist.dat; recreating
2016-02-26 15:15:29 Loaded 158 addresses from peers.dat 32ms
2016-02-26 15:11:32 Bitcoin version v0.12.0 (2016-02-17 09:40:03 +0100)
2016-02-26 15:11:32 InitParameterInteraction: parameter interaction: -whitelistforcerelay=1 -> setting -whitelistrelay=1
2016-02-26 15:11:32 GUI: registerShutdownBlockReason: GetProcAddress for ShutdownBlockReasonCreate failed
2016-02-26 15:11:33 Using OpenSSL version OpenSSL 1.0.1k 8 Jan 2015
2016-02-26 15:11:33 Using BerkeleyDB version Berkeley DB 4.8.30: (April 9, 2010)
2016-02-26 15:11:33 Default data directory [editted out]
2016-02-26 15:11:33 Using data directory [editted out]
2016-02-26 15:11:33 Using config file [editted out]
2016-02-26 15:11:33 Using at most 125 connections (2048 file descriptors available)
2016-02-26 15:11:33 Using 2 threads for script verification
2016-02-26 15:11:33 Using wallet wallet.dat
2016-02-26 15:11:33 init message: Verifying wallet...
2016-02-26 15:11:33 CDBEnv::Open: LogDir=[editted out] ErrorFile=[editted out]
2016-02-26 15:11:37
2016-02-26 15:11:37 Bitcoin version v0.12.0 (2016-02-17 09:40:03 +0100)
2016-02-26 15:11:37 InitParameterInteraction: parameter interaction: -whitelistforcerelay=1 -> setting -whitelistrelay=1
2016-02-26 15:11:38 GUI: registerShutdownBlockReason: GetProcAddress for ShutdownBlockReasonCreate failed
2016-02-26 15:11:39 Using OpenSSL version OpenSSL 1.0.1k 8 Jan 2015
2016-02-26 15:11:39 Using BerkeleyDB version Berkeley DB 4.8.30: (April 9, 2010)
2016-02-26 15:11:39 Default data directory [editted out]
2016-02-26 15:11:39 Using data directory [editted out]
2016-02-26 15:11:39 Using config file [editted out]
2016-02-26 15:11:39 Using at most 125 connections (2048 file descriptors available)
2016-02-26 15:11:39 Using 2 threads for script verification
2016-02-26 15:11:39 Using wallet wallet.dat
2016-02-26 15:11:39 init message: Verifying wallet...
2016-02-26 15:11:39 CDBEnv::Open: LogDir=[editted out] ErrorFile=[editted out]
2016-02-26 15:11:39 scheduler thread start
2016-02-26 15:11:39 Error: Couldn't open socket for incoming connections (socket returned error An address incompatible with the requested protocol was used. (10047))
2016-02-26 15:11:39 Bound to 0.0.0.0:8333
2016-02-26 15:11:39 Cache configuration:
2016-02-26 15:11:39 * Using 2.0MiB for block index database
2016-02-26 15:11:39 * Using 32.5MiB for chain state database
2016-02-26 15:11:39 * Using 65.5MiB for in-memory UTXO set
2016-02-26 15:11:39 init message: Loading block index...
2016-02-26 15:11:39 Opening LevelDB in [editted out]
2016-02-26 15:11:39 Opened LevelDB successfully
2016-02-26 15:11:39 Using obfuscation key for [editted out]: 0000000000000000
2016-02-26 15:11:39 Opening LevelDB in [editted out]
2016-02-26 15:11:39 Opened LevelDB successfully
2016-02-26 15:11:39 Using obfuscation key for [editted out]: 72046a1e7622fad5
2016-02-26 15:11:48 LoadBlockIndexDB: last block file = 197
2016-02-26 15:11:48 LoadBlockIndexDB: last block file info: CBlockFileInfo(blocks=365, size=131274522, heights=330521...330993, time=2014-11-18...2014-11-21)
2016-02-26 15:11:48 Checking all blk files are present...
2016-02-26 15:11:48 LoadBlockIndexDB: transaction index disabled
2016-02-26 15:11:48 LoadBlockIndexDB: hashBestChain=00000000000000001639f0ef7eb082b57e48f33baeb9082a7ab07ef3ef7df130 height=330922 date=2014-11-21 00:37:07 progress=0.450085
2016-02-26 15:11:48 init message: Verifying blocks...
2016-02-26 15:11:48 Verifying last 288 blocks at level 3
2016-02-26 15:12:05 No coin database inconsistencies in last 36 blocks (26535 transactions)
2016-02-26 15:12:05 block index 25562ms
2016-02-26 15:12:05 init message: Loading wallet...
2016-02-26 15:12:05 nFileVersion = 120000
2016-02-26 15:12:05 Keys: 0 plaintext, 265 encrypted, 265 w/ metadata, 265 total
2016-02-26 15:12:05 wallet 203ms
2016-02-26 15:12:05 init message: Activating best chain...
2016-02-26 15:12:06 UpdateTip: new best=000000000000000012e7c144fc1c1038c2e7826033b8c9739e5e690b8bf40b91 height=330923 log2_work=81.519843 tx=51953838 date=2014-11-21 00:49:03 progress=0.450095 cache=0.4MiB(1228tx)
2016-02-26 15:12:08 UpdateTip: new best=00000000000000001acb1484131a0b69c7666e1a9b94e483babae59adf1fe160 height=330924 log2_work=81.519915 tx=51954895 date=2014-11-21 01:02:32 progress=0.450111 cache=15.2MiB(4216tx)
2016-02-26 15:12:11 UpdateTip: new best=000000000000000005357156756d6576017e084a6ad8505fd2721feb79773b6c height=330925 log2_work=81.519987 tx=51956910 date=2014-11-21 01:56:55 progress=0.450153 cache=17.7MiB(8185tx)
2016-02-26 15:12:13 UpdateTip: new best=00000000000000001062194213863dab2ef62cb1f7715329927c6d24dc0dc0fd height=330926 log2_work=81.520059 tx=51957644 date=2014-11-21 01:57:29 progress=0.450161 cache=21.0MiB(9680tx)
2016-02-26 15:12:15 UpdateTip: new best=00000000000000000a99e0837981a3ffb45b20b14a4f30e6be51eb014a69a850 height=330927 log2_work=81.520131 tx=51959086 date=2014-11-21 02:14:09 progress=0.450183 cache=22.4MiB(11784tx)
2016-02-26 15:12:17 UpdateTip: new best=0000000000000000178e4ae780a4e48f28c1cf6e061167b92e3ee1f75e166a37 height=330928 log2_work=81.520203 tx=51960689 date=2014-11-21 02:40:51 progress=0.450211 cache=25.6MiB(14222tx)
2016-02-26 15:12:17 mapBlockIndex.size() = 400090
2016-02-26 15:12:17 nBestHeight = 330928
2016-02-26 15:12:17 setKeyPool.size() = 98
2016-02-26 15:12:17 mapWallet.size() = 307
2016-02-26 15:12:17 mapAddressBook.size() = 64
2016-02-26 15:12:17 torcontrol thread start
2016-02-26 15:12:53
I give 0.12 a fail stamp, sorry.