If Your PC Won't Boot, Replacing the CR2032 (CMOS) Battery Might Fix It

TL;DR#

• Replacing the CR2032 fixed the following situation for me.
  • I tried to boot an old PC (almost 10 years old) and it wouldn’t even show the BIOS screen.
  • Pressing the power button gave me one of the following two patterns.
    • The LED lights up, the fans spin, and the LAN port lights come on, but the screen stays pitch black.
    • Pressing the power button does nothing at all: no LED, no fans.
• Reseating the RAM, clearing the CMOS, unplugging and replugging all the cables, and other fixes didn’t help.
• After I swapped in a fresh CR2032, it booted like nothing had ever happened.

Background#

There was a PC from about 10 years ago asleep in my closet, and I tried to resurrect it as a home server.

The motherboard is an ASRock B250M Pro4.

The CPU is an Intel Core i3-7100, with 8 GB of RAM and a 1 TB HDD.

On top of that, I added a regular 250 GB SSD I had lying around (it actually had a “DEAD” sticky note on it, but I hooked it up as a long shot and it was recognized just fine) and a 500 GB NVMe SSD as the boot disk.

I installed Proxmox VE and got as far as running virtual machines. Then I unplugged it and moved it to start proper operation, and that was where the trouble began.

Symptoms#

I connected power, the LAN cable and HDMI, then pressed the power button. The LED lights up, the fans spin, and the LAN port lights come on. But nothing shows up on the screen.

Proxmox should boot by itself without any input, but when I tried to open the Proxmox web UI from another PC on the network, there was no response.

When I powered it off and pressed the power button again, this time neither the LED nor the fans reacted at all, and it turned into a complete paperweight.

Every time I unplugged and replugged the power, I got one of those two patterns.

What Didn’t Work#

I started troubleshooting together with Gemini (the AI).

I tried all the usual fixes: reseating the RAM, pulling the battery to clear the CMOS, unplugging and replugging the cables, booting with a minimal configuration. Five hours went by with zero effect.

Gemini started to give up, too.

1
I see... so even the minimal configuration doesn't work.
2
That's... truly unfortunate. And I sincerely respect the patience and drive you've shown in sticking with this troubleshooting for so long.
3

4
I have to give you my final diagnosis.
5

6
If it won't boot even with a minimal configuration (CPU + one stick of RAM + motherboard + power supply), and clearing the CMOS has no effect, then unfortunately that almost certainly means that one of the main hardware components has physically failed.
7

8
Static electricity during the move, cracked solder joints on the board from small vibrations, or simply the end of its life... It's hard to pin down the cause, but it is definitely a physical failure, not a software problem.

What Worked#

Then it occurred to me that a worn-out CMOS battery might be the culprit. This PC wasn’t a custom build; it was a normal off-the-shelf machine. And I’d left it shelved for 2 years without using it, so there’s hardly any dust inside the case.

Since I didn’t build it myself, the connections should all be fine. It’s not badly worn out, so a failed power supply or other part seemed unlikely.

But the CMOS battery is a different story. It exists to hold the BIOS settings, so it steadily drains. 10 years is plenty of time for a battery to run out.

So I searched for something like “What happens if CMOS battery is gone”, and the following Reddit threads came up.

[Discussion] Just a reminder that a dead BIOS battery can prevent your PC from booting

Just as an FYI, a dead CMOS battery can prevent your PC from booting

Apparently, in extremely rare cases, a dead CMOS battery makes a PC refuse to boot. Plenty of people said “it’s only for saving BIOS settings, so it can’t be related,” but it looked worth trying. If this solved it, I’d save close to 40,000 yen with an investment of about 100 yen (less than $1).

I pulled out the CR2032 coin cell and tried sandwiching it against a random LED, and it didn’t light up. The battery really did seem to be dead. I opened a spare CR2032 from my stock, swapped it in, and it booted without a fuss!!!!

(My display is filthy.)

Five hours after I started troubleshooting, at 5 a.m.

I have no idea why this fixed it. Did the dying battery leak a faint current and mess up the boot process…?

According to Professor Gemini,

In general, when the CMOS battery voltage drops extremely low, the motherboard chipset may not initialize properly, and the POST (Power-On Self-Test) process may fail to start. This is likely why even the BIOS screen wasn’t displayed.

apparently.

My savior.

It worked just by swapping in a new one.

Summary#

So, if you end up in the situation described above and it’s an old PC, try replacing the CR2032 battery.

I’ll write another article about the whole home server build.

↑Made with nano-banana.