I have 706Gb free space out of 869Gb. Thats about 160Gb's of space that im using.
I doubt its the hard drive
it's less about the space on the hard drive and more about a clean start
and if you're using windows (which it sounds like), you could probably swap to something like Ubuntu and see if that's faster
you haven't really told us the purpose of it yet, if you're just using it to host things you could go with a headless version of Ubuntu, if it's for more than just internet browsing (gaming), then windows might be needed
Linux works for gaming for the most part. I haven't gotten Victoria 2 to work, but otherwise I've gotten every game I've tried to work just fine on Debian with WINE. Still, I wouldn't recommend it if you don't want Linux for other reasons.