If you’re able to recover even a handful of files and the drive isn’t causing Windows to crash, I suspect your only problem might be damaged partition info. It happens, especially when a drive with write caching enabled disappears from Windows Explorer but reappears after a reboot. The cause could be an aging or inadequate PSU, bad cables or spotty connectors, voltage fluctuations, bad/corrupted controller drivers, etc., and not necessarily a damaged HDD.
I’ve used GetDataBack in the past to recover data from toasted partitions. It basically scans the drive sector by sector to recreate the missing partition–by reading the drive using this partition overlay, you can copy your files onto a known good media.
Anyway, just letting you know what’s worked for me.