Can't close window with X button

New here, looking forward to reading through some of the threads here and learning more about Windows 7.

I've been running RC1 since it became available, and recently I've added 2 other user accounts on my main PC. These 2 accounts seem to have the same problem: neither of them allow you to "x-out" of a window by clicking the red X up in the right hand corner to close the window.

It's quite an annoying problem, and I can't seem to word the problem just right to get an answer from Google. Hoping somebody here can point me in the right direction.

Thanks!

You could try the System File Checker:

"Right click on cmd and select Run as Administrator. Once the Command Prompt window open up type sfc /scannow"

(Taken from HERE)

many thanks!