Computer won't boot. Need boot disc

Hello,
I am trying to help my neighbor with their computer. They have a Dell computer they bought in 2000 with Windows Me installed and later upgraded to XP. The problem is that somehting happend to the computer where it will no longer boot up. The computer gets stuck in the boot sequence where it is looking for a boot disc in the "A-drive" My neighbor has never created a boot disc, can a boot disc be made on another computer to boot theirs? I tried to access the ROM to change the boot sequence settings but the function keys are not being recognized. Any suggestions to help my neighbor would be appreciated.

Thanks,
Steve