I tweaked the BIOS features on my PC (which uses a Giga-Byte Technology GA-7VAXP motherboard), and when I restarted the system, it wouldn't perform a power-on self test (POST). I know that I need to clear the system's CMOS, and the printed circuit board (PCB) refers to a jumper (which is even labeled CMOS Clear), but the jumper pins aren't present. I've searched the manual and Giga-Byte's Web site but can't find any instructions for accomplishing this task. How do I clear the CMOS?
Your motherboard isn't the only one that causes this confusion. If you're prone to tweaking your system BIOS settings (e.g., overclocking, aggressively tuning RAM timing), you're probably no stranger to nonbooting systems. Some systems let you use CMOS clear jumpers to restore CMOS default settings; other systems also—or instead—offer a keystroke that you can press when you power on the system. For example, some older systems used the Insert key for this function. To my knowledge, however, Giga-Byte boards offer neither of these options, so you need to use the third method: removing the juice.
As you might know, an onboard system battery (on most modern motherboards, this battery is a round, thin, lithium-cell battery) backs up CMOS memory. To clear CMOS memory, disconnect the AC power from the system's power supply, then disconnect the backup battery on the motherboard (you can usually just pop out the battery). Wait 10 to 15 minutes, then try booting the system again. The system should boot normally, with factory-default CMOS settings. If the system won't boot, wait another 10 to 15 minutes and try again; keep repeating the process until the system boots. Some systems can take as long as 1 to 2 hours after you disconnect the battery to clear, but in most cases one or two cycles does the trick.
