If all else fails, consult a professional data-recovery service — weigh cost vs. potential value.

Your wallet has used all pre-generated addresses. This is common after an update. Fix: Open the console (Help > Debug Window > Console) and type:

The wallet.dat file is a robust but sensitive component of the Bitcoin Core architecture. Its "update" process is seamless in modern versions thanks to HD wallet standards, but the risks of file corruption and accidental overwriting remain high.

Navigate to your data directory. If you have used the -datadir flag, go there. Otherwise, use the default path.