You can reset the BIOS back to defaults:
Clearing the CMOS
1. Power down the workstation and unplug the power cord.
2. Open the workstation chassis. For instructions, refer your workstation chassis documentation.
3. Move jumper (J2C1) from the default operating position (covering pins 1 and 2) to the reset/clear position (covering pins 2 and 3).
4. Wait five seconds.
5. Move the jumper back to default position (covering pins 1 and 2).
6. Close the workstation chassis and reconnect the AC power cord.
7. Power up the workstation.
The CMOS is now cleared and you can reset it by going into the BIOS setup.
(taken from the TPS, page 118 at Intel® Workstation Board S5520SC - Technical product specification )