Hmmm. Seems it was the wrong seed.
In this case I recommend that you migrate to a wallet who's seed you know by sending all bitcoins from the old wallet to the new one. 
Topic: Ack! Restored Wallet Empty!? (Read 566 times)
Hmmm. Seems it was the wrong seed.
Please restoe the wallet again from the seed.
(You can have a second wallet parallel to your default_wallet.)
After restoring make sure that it synchronized.
After it successfully synchronized (green icon in the bottom right).
Check if there are any transaction in your wallet.
Also check if you have the same addresses like in your default wallet.
Do you have the same addresses but no transactions?
Or do you have completely different addresses?
In the first case we need to go deeper to check why the transactions do not show up.
In the second case you have the wrong seed. Either find the correct seed or transfer all your bitcoins to the new wallet that you created with this seed.
Backing up the file is possible but it is safer to also know the seed to your wallet.
(You can have a second wallet parallel to your default_wallet.)
After restoring make sure that it synchronized.
After it successfully synchronized (green icon in the bottom right).
Check if there are any transaction in your wallet.
Also check if you have the same addresses like in your default wallet.
Do you have the same addresses but no transactions?
Or do you have completely different addresses?
In the first case we need to go deeper to check why the transactions do not show up.
In the second case you have the wrong seed. Either find the correct seed or transfer all your bitcoins to the new wallet that you created with this seed.
Backing up the file is possible but it is safer to also know the seed to your wallet.
I also had this problem. (Related topic here: https://bitcointalksearch.org/topic/help-electrum-wallet-empty-812737)
SITUATION:
I tried restoring a wallet using those twelve words I'd written down and it came up empty! This was a terrifying experience.
TECHNICAL:
I created the wallet 2-3 years. I think the version was 1.9.8, though I'm not certain. Now, I'm using 2.5.2.
MY COMPETENCE:
I've taught people to do Electrum wallet backups at a local meetup, so I'm pretty confident in my abilities. I also restored the wallet successfully about a year ago.
RESOLUTION:
I had a digital copy of the wallet saved on my super secret flash drive. I renamed it from "electrum.dat" to "default_wallet" and my great relief, it opened and all my bitcoins were there.
DEAR DEVS:
I've recommended Electrum in the past and want to continue recommending it. If there's any information I can provide to you so that you can trouble shoot this problem, please let me know via PM.
SITUATION:
I tried restoring a wallet using those twelve words I'd written down and it came up empty! This was a terrifying experience.
TECHNICAL:
I created the wallet 2-3 years. I think the version was 1.9.8, though I'm not certain. Now, I'm using 2.5.2.
MY COMPETENCE:
I've taught people to do Electrum wallet backups at a local meetup, so I'm pretty confident in my abilities. I also restored the wallet successfully about a year ago.
RESOLUTION:
I had a digital copy of the wallet saved on my super secret flash drive. I renamed it from "electrum.dat" to "default_wallet" and my great relief, it opened and all my bitcoins were there.
DEAR DEVS:
I've recommended Electrum in the past and want to continue recommending it. If there's any information I can provide to you so that you can trouble shoot this problem, please let me know via PM.
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