to "get things going" this 'might work':
Can I just simply copy the whole "xampp" directory from the old hard disk to the new hard disk even though the versions are different?
DO NOT MIX VERSIONS
just copy the whole nine yards, and get rid of any new install on the new drive
when copied over, run 'setup-xampp.bat' that is in the root of the XAMPP folder.
HOPEFULLY - you will learn the word 'backup'.
Get a flash drive and periodically backup/copy