I apparently got a virus (probably via the net) but neither Avast nor AVG found it. Eventually I stopped trying to disinfect and took drastic action. Full reformat and reinstall. This was on Sunday. Today it reappeared - no I have not reinstalled anything obviousy dangerous (and my virus scanners on highest protection still find nothing) - The effect are - bell dinging when cursor moved, increasing bell dinging, graphics corrupted, strange effects when trying to use cursor, wrong actions on click eg click on file menu opens a preview, and inability to start avast or eventually anything. This continued dispite reboots (sometimes having to shut machine off) for at least 3/4 hour. Eventually on one reboot I started explorer - got to programs (tho it usually would not let you) and started avasti. The effects ceased (possibly coincidence) at once but avast found no virus? Help - what have I got - and how do I cure it?