Jade, we're not here to be your 24/7 tech support team.
I mean, no one else has trouble with the concept of capturing their background image. So obviously no one here knows what you are doing wrong, as it's really not that hard of a thing to do.
The F lock button is irrelevant to this problem - BUT, what it looks like is a button that says "F lock" on it, suprisingly. It's only fitted on keyboards where the various F keys, F4, F5, etc, have something like "New", "Open", "Reply", etc above where it says the F#.
lol, i did play the multiplayer a few times. Not a bad quake iii knock-off, i had fun with it. Only problem is I've tried to get on it lately and no one is ever on.