What do you mean by 'format'?
PC format - I reload my PC every 3 months or so. Do it with a hardware change/upgrade. But I back-up the wallet.dat on all the coins and re-load them.
So you have the old (untouched) wallet. You tried using that?
Yes, with that the QT keeps crashing while trying to load the blockchain. So I loaded the blockchain with a new wallet and swapped from there. After some time the QT eventually loaded and from there I slowly tried to make a transfer to a wallet on my second PC. Moving slowly down in value from said 5M, every failed transfer crashed the QT. I finally made a transfer of 100k and then the QT has crashed along with the wallet. Whichever PC I load it on it comes up as a zero balance.
I'm left with the original wallet.dat and a file called: wallet.1413731410.bak
Salavage wallet while loading the QT does not work and I have come to the conclusion that I will have to mine them again, which is annoying but doable. I just would like to inform everyone that if you have a large amount from solo mining it is a wise plan to send them to a secondary wallet in larger amount transfers as the wallet seems to overload with hundreds of small transaction. This is not the only coin I have suffered it on. Giving everyone a heads up.
So don't sync the blockchain. Keep your network down, and dumpprivkey for all your addresses.
Import those private keys to your new wallet (or multiple wallets) and then transfer them to another address.
Another alternative is to sync completely with a new empty wallet, and then copy the backed up wallet.dat.
Our devs are aware of this problem in many wallets. They're seeing to it why this happens.
We had these problems while testing KGW against the new difficulty retarget algo (we're benchmarking against KGW to see it's performance).