Pc not starting flashing red light

[Alan176]

When I turn this machine on the white light comes on and the fan starts. Then the fan stops and the red light flashes 4 times. Then there is a small delay before flashes 4 more times etc. The white light does not come on. This fault is not in the diagnosis list. 

[Prométhée]

hi

 HP EliteDesk 800 G1 Tower HP EliteDesk 800 G1 Small Form Factor HP EliteDesk 800 G1 Ultra-Slim Desk...

check

This section covers the front panel LED codes as well as the audible codes that may occur before or
during POST that do not necessarily have an error code or text message associated with them

maybe
Red Power LED flashes four times, once every second,followed by a two second pause.

Beeps stop after fifth iteration but LEDs continue until problem is solved

Power failure (power supply is overloaded)

OR
The incorrect external power supply adapter is being used on the USDT

1 Open the hood and ensure the 4 or 6-wire power supply cable is seated into the connector on the system board

2 Check if a device is causing the problem by removing ALL attached devices (such as hard, diskette, or optical drives, and
expansion cards).

Power on the system. If the system enters the POST, then power off and replace one device at a time and repeat
this procedure until failure occurs.

Replace the device that is causing the failure.
Continue adding devices one at a time to ensure all devices are functioning properly

3  Replace the power supply.
4. Replace the system board.
OR
The USDT power supply adapter must be at 135W and use the Smart ID technology before
the system will power up.

Replace the power supply adapter with the HP-supplied USDT power supply adapter