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Unresponsive or unstable systems can often be rescued by resetting the firmware BIOS to its default configuration. The BIOS is based around a CMOS memory that stores system configuration data on an EEPROM (electrically erasable programmable read-only memory) flash memory module. The method for resetting the BIOS to default values differs with the motherboard model, but the basic premise remains the same. The electrical supply to the EEPROM, from the motherboard's onboard battery, must either be removed or shorted to clear the stored memory.
Most motherboards feature a CMOS clear jumper, while others require the user to hold a key during boot to reset BIOS values. If specific instructions are not available, simply removing the CMOS battery for 15 minutes can reset most motherboards. If that isn't successful, shorting the positive-to-negative posts of the battery interface socket with a wire jumper or paper clip may speed up erasure.
If the battery is soldered to the motherboard, it may be possible to drain it by attaching a resistor, with impedance under 100 ohms, between the positive and negative battery poles. Be careful, though: if the motherboard doesn't support battery recharging, this will render the system useless. A new battery will have to be soldered in place of the drained one.
Flash updating of the system BIOS can often restore the default configuration. The command to force such an update option varies by vendor, but most boards featuring popular Award or AMI BIOS routines can be forced to reinstate original CMOS values with a flash and reboot. Upgrading the BIOS can also prove beneficial, as the latest code usually includes compatibility and performance updates.
All user-defined settings are lost once the configuration is reset to factory defaults. Retain a hard-copy version of all BIOS, jumper, and dipswitch settings, as configured when the system is operating in a stable manner. The task of writing down each setting can be tedious, but this extra work ensures your ability to restore the system if it should fail. If you lack a backup list, most motherboard user manuals recommend BIOS settings for common configurations, and most BIOS Setup interfaces contain a Restore to BIOS Defaults option. Reset all motherboard jumpers and dipswitches to their default or recommended values before booting a reset system.
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