First you need to back up of your all documents and files then format your computer and reinstall your OS and anti-virus.
after you reformat, back up and have an anti virus you need to be careful in dealing with surfing the net and scan all external devices before copying something.
Formatting the hard disk is the last resort if you can't get rid of a nasty virus. Some viruses can be removed manually. Try to change your antivirus software and see which works best for you. No antivirus software is perfect. But some perform better than the others.
Get AVG anti virus and scanned your computer and delete the virus that detested. Try also malwarebytes to delete something that cannot detect by your anti virus. OR REFORMAT your disk...
run a scan with Avast Antivirus one of the best out there , my XP has been running since 07 thanks to Avast ( i have tried norton , kaspersky and AVG all failed to stop viruses which Avast stopped )