Before restoring it, have you run virus checking software, spyware software, checked the hard drive for errors etc.? If you have, or you dont want to go down that route and want a clean slate, then reformatting the hard disk wold be the only way to "start afresh". The computer wouldn't understand to boot from original disk. Refortatting a hard drive wipes all data from that hard drive, so make sure everything you want saved is backed up (you said it is, so fine).
WARNING: Never reformat a hard drive unless you have the original Windows CD's at hand.
That said, there are many websites that can give you detailed instruction of how reformat the hard drive, followed by reinstalling Windows (the crucial part). Just type in "reformat hard drive" into google and print off any important pages for reference.
I would recommend doing the above as a last resort. You will lose the ability to print, use the internet etc. until you reinstall the software to run them. Firstly try the things I mentioned to start with, especially downloading an update driver for your graphics card. If you let me know the make of the card, I will post the link for the update driver for you.
Hope this helps.
