Welcome to Tom's Hardware Forums,
As to entering BIOS on your machine, tricky, here's what your manual has to say about that (pg 111)
"1 Turn on (or restart) your computer.
2 When the blue DELL™ logo is displayed, you must watch for the F2 prompt to appear.
3 Once this F2 prompt appears, press <F2> immediately.
NOTE: The F2 prompt indicates that the keyboard has initialized. This prompt can appear very quickly, so you must
watch for it to display, and then press <F2>. If you press <F2> before you are prompted, this keystroke will be lost.
4 If you wait too long and the operating system logo appears, continue to wait until you see the Microsoft® Windows® desktop. Then, shut down your computer (see "Turning Off Your Computer" on page 61) and try again."
So, in just the split second you are prompted, you have to hit F2 - how fun, it's like a game (see if you can catch me) or something.
BTW, your manuals are here
http://support.dell.com/support/edocs/systems/dime521/en/index.htm
Enjoy your game of catch the F2 window