Heaps of viruses corrupted files

fixer1950 sorta has the right idea. You do need an antivirus, but I disagree with his choice. Avast has a poor detection rate. You should use Avira if you want a free antivirus or Nod32 if you don't mind paying for one. To get rid of the viruses, run malwarebytes and superantispyware. Then install either Avira or Nod32.
Keep all your software up to date, keep the Windows Firewall on and run ccleaner once a week or so and you should be fine.

IF YOU WISH NOT TO LOSE THE DATA AND CLEAN UP YOUR SYSTEM FROM VIRUSES AND SPYWARES THEN FOLLLOW THE LINKS BELOW AND INSTALL THE SOFTWARES AND RUN A COMPLETE SYSTEM SCAN AND EVERYTHING WOULD BE BACK IN PLACE..

SUPERANTISPYWARE
http://www.filehippo.com/download_superantispyware/

AVG-ANTIVIRUS
http://www.filehippo.com/download_avg_antivirus/

CCLEANER
http://www.filehippo.com/download_ccleaner/

TROJAN REMOVER

http://www.scanwith.com/Trojan_Remover_download.htm

Rate All The Solutions Accordingly...(",)

That's what happens when you don't use the protection that averyone has been talking about for the past 10 years.
Get Avast anti virus and keep it updated automaticaly and run it. Get some frww online malware and spyware programs and use them. Use a firewall. Run a registry cleaner. This will get you running like a new machine but, EVERYTHING must be kept updated, not just when you run into a problem. They're easier to prevent, than they are to fix. I bought a laptop with issues for $100. It had 196 viruses and tons of spyware, addware and other malware on it and the registry was 3 times the size it should have been. It took 2 days of cleaning but, It runs like a new machine and the previous owner wants it back. His new laptop is slowing down. He doesn't use all the protections I mentioned and I'll buy his used laptops for $100 any time.

You can try to fix it or just install a new operating system.