F5 turns computer blink black

When i refresh my computer the desktop turns black for sec's and again comes to normal. When i restart the blank screen appears with desktop items and after 2-3 sec the wallpapers appears. When i drag the folder in the desktop it shows the dragging of the folder like: many folders behind the original and when dragging done it disappears. Kind of weird problem cannot explain this in more detail. :) Using AVG anti virus and no virus threats seen....using C cleaner and other system scanner no threats found. 2GB ram with minimum XP softwares on the computer.