To Reformat or Not

I've long suffered with having to put up with how slow my PC works. Am not really sure if it's because of the size of my files or if it has a lot of worms, Trojans, viruses and what have yous. I'm still thinking if I need to reformat the PC or not. I'm afraid I may not get all the applications and software I have installed in it...*sigh*...i still have 2 more days left to reconsider.