Recovering CMOS then won't reboot.

[trustedstar1]

Dark screen. Did a Bios recovery which was successful. Then I get a CMOS 502 error and pressed Enter like it said to Restart the laptop. Would not restart. There is No coin battery for the CMOS. All is powered by main battery. Battery charges up still. Something is corrupt but not for sure. Any ideas community?

[Max3Aj]

@trustedstar1, Welcome to the HP Support Community – it’s great to have you here!
 

I appreciate you taking the time to share your question. I'm more than happy to assist with this and provide a solution that works for you.
Based on your description, successful BIOS recovery followed by a CMOS 502 error and failure to reboot, this issue typically points to a corrupted or invalid CMOS checksum. Since your HP laptop doesn't have a removable coin-cell battery and relies on the main battery, here are steps you can follow to resolve this:

Perform a CMOS Reset (No Coin Battery Required)

HP laptops without a coin-cell battery use a key combination to reset CMOS:

• Plug in the AC adapter.
• Turn off the laptop and wait at least 5 seconds.
• Press and hold the Windows key + V key.
• While holding these keys, press and hold the power button for 2–3 seconds.
• Release the power button, but keep holding Windows + V until:
  • You see a CMOS reset screen, or
  • You hear beeping sounds.

If successful, the system will reset CMOS values and restart. You can then access BIOS and diagnostics.

Restore BIOS via USB (if CMOS reset fails)

If the laptop still won’t boot, try restoring the BIOS using a USB recovery drive:

• Use another PC to download the latest BIOS for your laptop from HP Software & Driver Downloads.
• Copy the BIOS file to a USB flash drive.
• Insert the USB into the affected laptop.
• Power on the laptop and immediately press Windows key + B, then hold the power button for 2–3 seconds.
• Release all keys and wait. The screen may remain dark for a minute before BIOS recovery begins.

HP Notebook PCs - System BIOS Recovery has occurred | HP® Support

Update BIOS (if system boots)

If the system boots after CMOS reset or USB recovery, immediately update the BIOS to prevent recurrence:

• Go to HP BIOS Update Instructions
• Download and install the latest BIOS version for your model.

Additional Tips

• Ensure the main battery is charged and the AC adapter is connected during all steps.
• If the laptop still fails to boot, consider contacting HP Support or visiting a service center for hardware diagnostics.

You may refer to this document - HP PCs - 500, 501, or 502 error displays on a black screen | HP® Support

I hope your issue is now resolved. If not, feel free to reply and we’ll continue helping until everything’s sorted!

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Cheers,

Max3Aj

HP Support