I used either CTRL+PRTSCN or ALT+PRTSCN to grab a screenshot, but when I paste the screenshot I don't get what I wanted or I get nothing at all. What could be the problem?
Some keyboards have a feature called "function lock" that changes the behaviour of the keys F1 to F12 and the PRTSCN key and the Pause/Break key.
You may need to turn off the function lock controls on the keyboard using the F-Lock key to get the PRTSCN combinations to work the way you would expect.