jenk

Seriously. I got it from the Microsoft Support Knowledgebase.

From the KB article:

SYMPTOMS
When you try to print the contents of the screen for a console application that is running in full-screen mode in Microsoft Windows XP, nothing is printed. If you repeatedly press PRINT SCREEN, Windows XP may stop responding. You may have to restart the computer.

CAUSE
This problem occurs because the Win32K.sys file does not release the bitmap that is stored in the clipboard when you press PRINT SCREEN. Eventually, this memory leak causes the computer to stop responding.

Really, you have to wonder if someone's cat was involved in finding this one...