And what does the error said?
It could be vague sometimes but the error should be able to point you to the issue.

For example: if it says "Data is not in recognized format", the wallet.dat may be corrupted but it doesn't tell if the keys in it are damaged.
That case might be solved by using "salvage" command of Core's bitcoin-wallet tool if the wallet has intact keys.
Note: if you're going to research how to do that method, please use a copy of your wallet.dat file and not the main backup.