Common issues in Windows...
The file was accidentally renamed to something like:
- wallet
- wallet.txt
- wallet.txt.dat
- wallet.dat.txt
- wallet.wallet.dat
(Or some other variation) and Windows is hiding this invalid name from you.
You may need to use a command line in Windows and look at a directory listing to make sure that the file is actually named correctly. Bitcoin Core will look for the exact filename: wallet.dat
The wallet.dat is placed in the wrong folder for your version of Windows. Double check to make sure that you know what folder it should be in, and that you actually put the new file in that folder.
One way to be certain that you are looking at the correct folder is to:
- Shut down Bitcoin Core
- Remove all copies of wallet.dat from the folder that you think is the correct folder
- Start up Bitcoin Core
- If Bitcoin Core can not find a wallet.dat in the expected folder it will create a NEW wallet.dat
- Shut down Bitcoin Core
- Look in the folder where you previously removed all wallet.dat files. There should now be EXACTLY 1 wallet.dat file. If there is not, then you are probably looking in the wrong folder.
You are accidentally restoring the wrong wallet.dat.
It might be possible that you accidentally put the litecoin wallet.dat file in the folder for Bitcoin Core, or it might be possible that you are accidentally trying to restore a VERY old backup and that you need a newer backup, or it might be possible that you confused your backup wallet.dat with a new wallet.dat.
Double check that you are using your most recent wallet.dat backup file from Bitcoin Core. If you still have access to the original wallet, and that original wallet still shows the correct balance, then try calculating a checksum on that original wallet and on the backup you are trying to restore. Make sure the checksums are identical.