Not able to enter set-up with F2 button during boot sequence

I have a Dell Optiplex GX1, Pentium III 500MHz. I bought a Dell SK-8125 key board. It has a USB plug. Old k/b had a ps/2 plug. I down loaded driver, pluged it in, and all seemed to work. When I tryed to enter the set- up program with the F2 button, nothing happend. I was plugged into a USB 2.0 PCI card port. I moved it to one of the existing USB ports on the systems board. Same problem. I down loaded the driver again from dells web sight. Removed origional driver, installed new and Same problem?