System unit no led light but fan running

[Jeriko]

when I on the power supply it automatically on the system even thou I didn't press the power button yet. 

There is no led light on the power button but the fan is running.

[Echo_Lake]

@Jeriko
Thank you for posting on HP Support Community.

• Did this happen after a recent window or software update?
• Have you made any hardware/software changes?
• Have you tried any troubleshooting steps?
• Have you tried with different monitor or display?

While you respond to that, let's try this workaround.

1. Unplug all cables except for the power. Write down each cable location if you do not already know where it connects.

2. With the power cable removed press the Power button on the front of the computer for 5 seconds.

3. Remove the screw(s) that retain the panel or cover from the rear of the computer.

4. Slide the side panel off from the rear of the computer.

   

5. Gently press down on the outside edges of cards and memory modules that are inserted into the motherboard to better seat them. Do not press too hard.

6. Gently press down on the connectors of the flat ribbon cables to seat them.

7. Replace the side panel and screw(s), reconnect the computer cables, and turn on the computer.

8. If the monitor still displays a black screen or displays a No signal message, the video hardware may be faulty and needs to be replaced or serviced. 

Hope this helps! Keep me posted for further assistance.
Please click “Accept as Solution” if you feel my post solved your issue, it will help others find the solution.