Vista 64 bit: All screenshots are stuffed up

hi everyone
I'm having a rather unusual problem with windows vista
Whenever i press the print screen button or use the snipping tool, all the screen shots come out all gray (except the very top of the screen, where i can just see the top of the window)
The screen reminds me of the user account control screen, the screen vista goes to whenever you try to open a .exe file or file vista doesnt recognise
I've tried using 3rd party screen shoting tools and they do the same thing
I've even tried changing the register to stop the user account control screen going to that gray screen but nothing seems to work
Thanks in advance for the help