My PC's hard drive is a graveyard of old legacy files of things that don't exist anymore, going back several generations

[canetoad]

11. As mentioned above

And this is a really good idea and can be a lifesave:

Partition your hard drive into:

1. Operating system and programs
2. Your own stuff

Reformat and reinstall the most recent version of windows you have or can run on what will become your C drive. Check your current system and programs folders for size to give you some idea of how large the partition should be. I'm good with about 300 gig but if you run some huge games and programs you may need more.

The other 700 gb or so becomes your own personal stuff. There are ways to move the built in users folders onto this drive via....
User Folder
Properties
Location - set new location on your new D drive

Once you have done this, a big clean out and reinstall of a bloated operating system becomes a breeze - something that can be done in a couple of hours, including program installation. Your own personal stuff remains untouched through the ages!