Also, as Jono said, make sure you actually move your personal stuff rather than copying it. Otherwise it will still take up your hard drive space.
Ye - you wouldn't believe how many times I have run into that one...
Sorry if it sounded a little flippant - wasn't meant to be. I generally try to rule out the obvious stuff before getting on to the complicated/worrying stuff (in most things - not just computers) - takes seconds and sorts out a surprising number of problems
TBH I am not really up on windows, but Windows 7/8 don't seem to be too bad with clogging up stuff - mind you, I *may have turned off the restore stuff when we got the computer - was quite a while ago.
Disc drives are pretty monsterously sized these days..
You can probably still get TreeSize - I think it has a free version - it will analyse your disc ahnd show you graphically what is taking up the space.