PC long-beeps once then turns off

[RogueNimbus]

Hi 😊 OMEN 25L.

My pc powers on then long-beeps once then powers off. Just a night before this incident, it turned on but all of the peripherals, including the monitor, did not light up. The only thing that I could see was responsive was what was inside the pc itself (ram sticks, all fans, omen logo light and heatsink fan light, WD black SSD light)

A couple days before this, I needed to press the power button twice for it to turn on.

If this extra context is helpful: recently the power company that is providing me electricity has an issue with fluctuating voltage which shorted a couple of my UPSs (that's a separate matter I'm trying to get them to fix)

Any help on what component might be the culprit will be greatly appreciated 🙂 

Thank 

[Bill_To]

Greetings @RogueNimbus 

Welcome to the HP Forum.

The power utility problem is very good to know. Fluctuating voltage can take out any PC component connected to a dirty power source.

HP, at this Site, does not list one long beep error code at startup. But a severe power problem exists when a PC immediately shuts down after startup.

I can only suggest trying a different, known good, PC power supply (PSU) and a working UPS to see how it goes. It is not necessary to install the second PSU in the case to check for a good POST.

But verify the power utility is providing clean power before using a different PSU.

A no go using a good PSU would suggest problems with any of the PC components connected to the MB and any peripherals connected to the PC. 

And the MB may be in trouble. Even though you are getting a one beep error code at startup.

Try starting the PC with only the following components connected to the MB:

1. Power supply

2. CPU

3. One stick of RAM. Try each stick of RAM in each memory slot

4. Onboard graphics if your PC supports this

5. Or try a different graphics card

6. A working monitor

You might need a local PC Tech if you can't isolate the: faulty component or components.

Regards

[nobleaura]

A single long beep followed by shutdown on OMEN 25L usually points to a power supply or motherboard issue, especially given the recent voltage fluctuations you mentioned. The earlier symptom (needing to press the power button twice) also strongly suggests PSU instability or damage.

I recommend checking HP’s official beep code guidance here: HP Desktop Beep Codes & Startup Issues Guide

If possible, test with a known-good PSU first, as power surges often damage the PSU before other components.