After a full scan it found 4 wallets, 900 encryptet keys and 1800 unencrypted keys. It only imported those 306 keys from last time. 0 coins. Guess my coins are lost forever.

I made 4 or 5 backups back then. But I forgot about bitcoin for a while because of the low value, and one disk after another failed. I'm even pretty sure I made an online backup, but I can't find it anywhere...

Thanks for all the help though!