If it's a new pc, it's probably caused by some kind of drivers messing up with your processes. If you're sure you don't have anythign like Windows Blind, I suggest you try disabling a couple of software from your startup with msconfig until you find the culpirit.
I'm sorry I can'T help you personally on this right now but once version 4.500 will be released, if you continue to have the problem, I'll gladly analyse the problem with you.