so for the past couple days, my computer has slowed so bad that it takes a good couple minutes to perform a function on the computer. things like opening programs and what not. even to exit out of a window, i will hit the X and it will take it 3-4 minutes to close out. its showing that there is 100% CPU usage. i thought it was a virus so i did a scan (AVG free) and it turned up no threats. the only time i can use the computer is when i boot from "last known good configuration". even then i can use the computer for a good 10 minutes or so before it goes back to mind numbing slow. is there any suggestions or is reformatting my only way to fix this?