Yeah, and what are your computer specs...? 3% left on your drive, that shouldn't slow down text appearing on the screen unless...eh...
And as they said: use an anti-spy/adware program (link to adaware is in my signature)...you can clear out temporary files of various sorts (internet, windows etc) and lost file fragments window's found when scanning your drive for errors. Then defrag...(they recommend having 15% free drive for this.)
And of course, (depending a lot on your PC), you can only have very good performance while doing so much.
Reformatting will work, though it's a fairly big hassle trying to back everything up, re-download updates/programs and install them...if you're up for that. When I had windows 98, I reformatted, it seemed, every 4-5 months as it got sluggish after awhile, but with Windows XP, though I only use it half the time, I've had it for three years (about) now, and never reformatted. Linux is a nice choice too, specficially slackware (muahaha...not really, unless you're into the dos based stuff
, at least partially)