Power button LED blinking (for minutes/hours), not booting nor reacting to long press

[JJ-from-Germany]

Hey everyone,

I'm facing power-on problems with my three-year-old notebook, which occured more often in the last months and currently nearly every boot. Already tried several troubleshooting hints but nothing helped. Would be glad to get help here. Will describe the problem first and what I've already tried to solve afterwards (sorry, this is  a very long message).
I have Windows and Linux installed as dual-boot, but the problem occurs before even booting into the Hardware/BIOS Setup menu, so I'm pretty sure this does not matter.

== Problem ==

A) When trying to power on the laptop, by pressing the Power button, the white LED on the power button ("Power LED" in the following) starts blinking (in an interval of a few seconds), but nothing else happens. For a few minutes, sometimes even for an hour or two, after that suddenly normal boot continues (fan goes on, power LED staying on permanently). (Long) pressing the power button during blink does not change that behaviour, and also does not turn off the blinking.
This issue occurrs lately nearly at every boot.
B) In some rare cases the laptop even seems to boot, indicated by the Power LED staying on permanently and the fan turning on, but nothing appears on the screen afterwards. In this state, the laptop is producing a noticeable amount of heat (fan going crazy and case getting warmer than during normal use). However if this case B) occurs, the Laptop can be turned off reproducibly by long-pressing the power button.
C) Some times after successful boot, the system clock is reset to midnight in some fixed day (currently September 4, every few weeks it steps forward to some fixed date in recent past). Whether this Problem C) happens seems to be independent of whether one of A) or B) occurred at boot before.
D) In some very rare cases, there was a BIOS corruption detected (as a blue box with white letters showed my after power on), and the recovery which the text pretended to try failed since „The BIOS recovery files cannot be found or the files are corrupted“. After Inserting a BIOS recovery USB stick created with that official HP tool on another windows machine, the BIOS recovery procedure worked successfully.

E) When powering off the Laptop with low battery (ca. 10%), and connecting it to the charger an hour later, the charging LED (next to the AC plug) did not turn on orange as usually when charging, also the Laptop did not turn on at all (not even a blinking of the Power LED).

== Steps I've tried so far ==

In those cases E) happened, I opened the case, disconnected the battery, connected the AC cable and powered on the Laptop successfully. After shutting down and reconnecting the battery, charging and booting also was succesful.

I guessed my battery might be broken, so I ran the complete HP hardware diagnostics suite (flashed on an USB Stick entered via F2 (ore some other F button?) on boot). No problems with my hardware were found, neither battery nor system board nor anything else.

I also updated the BIOS to the latest version, as I had to do in case D) happened anyway.

I ran the PC diagnostics tool on Windows, no Problem and no update was found.

I opened the case, removed the battery, loosened the heat sink and took a look on the system board (as far as I could w/o removing more parts which I didn't want to damage), hoping to find some small battery cell on the mainboard which could be discharged, as some forum posts on the internet suggested that – I found nothing, reassembled  my laptop and the problems continued.

Lastly, because the problem scenario A) occurred nearly at every boot, I removed the battery and kept using the Laptop on AC power only. (After battery removal the CMOS checksum was invalid, but this seems to be usual since I removed a hardware part.) That leads to the laptop reporting the invalid CMOS checksum at every boot after power disconnect (because I e.g. travelled to a friend), and the time reset problem C) occurring more frequently. But the problems A), B) (D and E are rare anyway) disappeared for one week. Sadly, since one day, the power on problem A) is occuring again, the battery is still removed since more than a week now.

== Conclusion ==

I would be very happy if here is some HP or hardware pro who can give me further advice. I'm happy to answer any troubleshooting questions.

As a last note: the device was not used for about a year, before I got it from a relative 10 months ago (another point why I guessed the battery may have become damaged).

Regards!

[Max3Aj · Accepted solution]

Hi there @JJ-from-Germany, and welcome to HP Support Community!

I'm glad to assist you today.

Thanks for the detailed breakdown, it’s incredibly helpful for diagnosing the issue. Based on your description, the symptoms point to a deep hardware-level issue, likely involving the power delivery system, BIOS/EC firmware, or embedded controller (EC). Let’s go step-by-step to isolate and potentially resolve this.

• Power LED blinking for minutes/hours before boot.
• No display output even when fans spin.
• System clock resets (suggests CMOS battery or EC issue).
• BIOS recovery prompt occasionally appears.
• No response when battery is low and charger is connected.
• Temporary improvement after battery removal, but issue returns.

Steps to Try:

Perform a Full EC Reset (Embedded Controller)

This can help clear any firmware hang-ups.

Steps:

• Disconnect charger.
• Remove battery (you’ve already done this).
• Press and hold the power button for 60 seconds.
• Reconnect AC adapter only (leave battery disconnected).
• Try powering on.

If this works consistently, the EC may be failing to initialize properly when battery is present or after deep sleep.
 

Check for EC Firmware Update

HP occasionally releases EC updates bundled with BIOS updates. You mentioned updating BIOS, but please confirm if the latest version includes EC firmware.

Official HP® Support

• Download the latest BIOS package.
• Run it from Windows (if accessible) or use the HP BIOS Update USB Recovery Tool.
• If already updated, try reflashing the BIOS, this can help if corruption persists.

Inspect CMOS Battery (RTC Battery)

The clock reset and CMOS checksum errors suggest the RTC battery (small coin-cell battery on the motherboard) may be dead or disconnected.

• This battery maintains BIOS settings and time.
• If it’s dead, the EC may fail to initialize properly.
• You mentioned not finding it, it’s often hidden under the motherboard or near the Wi-Fi card.

If you're comfortable, try locating and replacing it. Otherwise, a technician can help.

Test with Battery Reconnected but Disabled in BIOS

If the laptop boots reliably without the battery, but you want to keep it installed:

• Reconnect battery.
• Boot into BIOS (F10).
• Look for any battery-related settings (some HP BIOS versions allow disabling battery charging).
• Save and exit.

This avoids CMOS checksum errors while keeping the battery physically connected.

Run HP UEFI Diagnostics Again

Even if it passed earlier, run it again with battery connected and disconnected.

HP PC Hardware Diagnostics | HP® Support

• Create USB stick.
• Boot via F2 or ESC > Diagnostics.
• Run System Board, Battery, and Power tests.

Consider EC or Motherboard Failure

If all else fails and the issue persists even without the battery, the embedded controller or power delivery circuit may be failing intermittently.

In that case, please visit the nearest HP authorized service center, the service team will check and assist you. 
Kindly follow this link to locate the nearest HP service center: HP® Service Center Locator - Deutschland | HP® Support
(Select the country from the dropdown menu and enter the city name or pincode)

If the suggestions helped solve the problem, please let us know by clicking “Accepted Solution.” It really helps fellow users find quick answers.

A quick “Yes” also goes a long way in showing appreciation!

Take care and happy computing!

Best regards,

Max3Aj

HP Support

[JJ-from-Germany]

Thank you very much for the detailed help. I updated the BIOS Firmware again (did not find any update specifically including EC firmware). But the issue persists, so I'll contact a local HP service center.

[Max3Aj]

@JJ-from-Germany, Thanks for letting us help you out! 

If you have any more questions or need further assistance, please don't hesitate to ask. We're here to help! 

Thanks again for your confirmation, and we wish you an amazing day ahead! 

Regards, 

Max3Aj