Cant Print Screen

I know this isn't a hardware problem, but its close enough.

My problem is that just randomly while using my computer, my print screen button just stops working.
I use it to verify placement of items for css, so I need it.

Most of the time I have no problem using it after I turn on my computer, then randomly it just quits working in the middle of things.

Using the combination of ctrl, alt, and shift keys is useless.

A restart fixes the problem, so I just want it to stop coming back....

Jordan