Oblivion screenshot problem?

I am running oblivion on windows xp, and im well past all the recommended requirments. the game runs beautifully. unfortunatly, it wont let me take screenshots. i did change the file in the oblivion.ini from bAllowScreenShot=0 to =1, and i am on an administrator account, but when i get in game, nothing happens when i press the print screen button, and i have tested it on two different keyboards. any suggestions??