Slow

Do you mean (like when you first got the PC?) Or do you just want to get your speed back like it used to be?
To (Restore) the Pc you would put the restore cd in the cdrom & start the PC, the restore cd will start up & you follow the on-screen instructions. All personal data will be earsed.

To regain your systems speed.

1. Run a complete system virus-scan. Updated

2. Clean your windows from junk.

http://www.pctuneuptips.com/recommends/clean/?gclid=CPabho72g5ICFShMGgodgHiOUw
Or
http://www.pc-error-free.com/registry-clean.html
& or any one of these free programs:
http://www.topshareware.com/guide/hot/junk.htm

3. Run system Defrag. Click Start > Programs > Accessories > System tools > Defrag. When finished re-start the PC.

Good Luck & Best Wishes!