pc not turning on, white light blinking after pressing startup button

[Marta_]

when I try to turn my PC on, the fans start working as usual, and my keyboard and mouse lights turn on but the monitor doesn't.

Then, the light next to the startup button starts blinking white three times. 

Then a moment later it turns off entirely.

I've tried to 'Power Reset' my PC and it doesn't do anything.

I've tried to open up the thing where you press 'esc' multiple times, but then the PC beeps and my monitor stays black. so no luck there either.

It's a HP Z2 G9 TWR i914900K 32GB/1TB PC

[MysteriousMe]

Welcome to HP Support Community, @Marta_ 

Thank you for posting your query, I will be glad to help you.

Problem:
The PC powers on (fans, keyboard, mouse) but the monitor stays black.
After a few seconds, the power LED blinks white three times and the PC turns off.
A power reset does nothing. Pressing ESC causes beeps but no display.

What the 3-White-Blink Code Means

On the HP Z2 G9 workstation, 3 white LED blinks indicates a hardware initialization failure. The most common causes are:

BIOS corruption

Motherboard failure

CPU not initializing

RAM not detected

Because the PC shuts off after the blinking, the issue is usually the system board or BIOS, not just RAM.

Step-by-Step Troubleshooting

Perform the steps in this order.

1. Clear CMOS / Reset BIOS

This can recover a corrupted BIOS.

Disconnect the power cable

Hold the power button for 20 seconds

Open the side panel

Remove the CMOS battery for 5 minutes

Reinstall battery and reconnect power

Try powering on again

2. Reseat RAM

A poor connection can cause a boot failure.

Remove all RAM sticks

Install only one stick in the primary slot

Try to boot

If no change, test the other stick and other slots

3. Test Integrated Graphics

Your processor (i9-14900K) supports onboard graphics.

Remove the dedicated GPU

Connect the monitor to the motherboard HDMI/DP

Try to boot

If the system boots, the GPU is the problem.
If the system still does not display, continue.

4. Verify Power Connections

Check the 24-pin motherboard power connector

Check the 8-pin CPU power connector (near the CPU)
A loose CPU power cable can cause 3-blink shutdowns.

5. Evaluate System Board or CPU Failure

If none of the above steps change the behavior, the root cause is likely:

Motherboard failure (most common)

BIOS failure that cannot self-recover

CPU initialization failure (less common)

At this stage, the system will show no display and blink 3 times consistently.

I hope this helps.

Take care and have a good day.