Taskbar and icons blinking?

I have a dell computer with windows xp. My computer just started acting up. after startup everything appears fine then the taskbar and all my desktop icons will disappear( the only thing on the screen is my screen saver and whatever I have opened at the time. It will stay like this for a few seconds then reappear. this problem happens about every minute or so. I ran mcafee virus scan which came back clean. I have no clue what to do now. Please if anyone can help....