I think that my PC has downloaded a virus, although it has not been identified by either Norton or AVG, and threfore cannot be removed. The apparent virus attempts to make about 20 registry modifications, which destroy links and prevent .exe files from activation. Ad-watch identifies the potential changes and asks whether they should be blocked or accepted. However, clicking block does not prevent the changes. Failing to click either does prevent the changes, but leaves an ad-aware window continuously on the screen. If the changes are allowed to take place, I can only return to proper functionality by restoring a system volume info backup file. Any idea of how I might solve this without reformatting the hard drive?