It looks like your wallet.dat is still on your old disk. Just in case: you should have made a few backups (for instance on different USB sticks) already. If you didn't do that, you should do it before doing anything else.
Then, just copy your old wallet.dat.
You may want to upgrade your Bitcoin Core version (see
News link above this page). Your version is many years behind.
If the blockchain has been downloaded in prune mode, you have to download the blockchain again.
If it was pruned, he wouldn't have needed a larger hard drive.