When you use Ctr/alt/del to show running programs it sometimes take 2 or 3 clicks on each one to end the program. Try this again and see if you can close down some of your running programs. Then by a process of elimination find the one/s causing the problem.
If the above does not help, then boot your PC in safe mode and do an AVG scan from there. I think that AVG will still work from safe mode.
Also because you have AVG running, make sure from going into your BIOS that you don't have a DOS version of "anti-virus" program running as this will cause a conflict with AVG.