Stopped working how?
If you cannot use F2 during POST and get into BIOS Setup (Visual BIOS), the first thing to do is clear CMOS. Unplug the power cord, open the bottom of the chassis and unplug the CR2032 battery for 15 minutes.
Once you can get into BIOS Setup, use the F9 key to reset the configuration to defaults and then the F10 key to save this configuration and exit.
Hope this helps,