Check the CMOS battery if PC won't boot

If your desktop PC doesn't start, check the CMOS battery on the motherboard. The battery is usually CR2032, a round disc about $1 each.

The motherboard relies on the battery to store its settings. If the battery is weak or not present, the motherboard may refuse to post into BIOS.

The CPU fan spins for a while, louder than normal. The hard disks spin, the graphics card fans spin. Everything seems powered up and working, but still nothing shows up on the monitor. Then after a few seconds, the computer restarts itself and goes through the same cycle endlessly.

My best guess is the motherboard isn't loading its settings properly because the CMOS battery is low. Replacing with a new battery fixed the problem immediately.

http://pc-restorer.com/wp-content/uploads/2013/11/batteryCR2032replaced.jpg

Requirements to post into BIOS can vary depending on the motherboard. Usually the components to check if a PC won't boot are:

1. RAM
A stick of RAM with errors will prevent the motherboard from loading BIOS, 100% of the time. Test each Ram module individually. All sticks must be working. Even one bad stick will stop the boot.

2. Graphics Card
If the motherboard doesn't have integrated graphics, it won't start unless a graphics card is inserted (AND a monitor is connected and turned on in some cases!)

3. PSU
Obviously, there needs to be power going to the motherboard and components. Check the power cables are plugged in and no pins on the motherboard are bent!

4. CPU
Another obvious one. The processor chip needs to be installed for the computer to run. Again, make sure no pins on the motherboard touching the CPU are bent or broken.

5. CMOS battery
These things are supposed to last for a long time. On an old computer (3+ years) though, it might be time to replace the motherboard battery.

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