HP ProDesk 600 G3 infinite loop (screen ever black)

[shift74]

Hi everyone! The problem is the following:
I turn on the PC, the power led turns on, the fan starts and after about 20" it turns off and restarts automatically, all this cycle endless times and there is no way to enter the BIOS.

These are the attempts:
- I removed the power cable, held the power button for 30 "and removed the CR2032 battery to reset the CMOS
- With a keyboard attached I pressed (Windows Key) + B, the Power key for 2 seconds, I released the Power key
I don't know what else to try because having no input on the screen, no beeps, or anything else, I have no other elements to understand how to proceed, does anyone more experienced than me or who has run into the same problem know what else I can try?

[BeemerBiker]

Try a different memory stick.  It is possible the power on memory test (if any) fails to detect the error.  Frequently re-seating the memory fixes the problem.

Another possible problem I have seen is power surge when a supply is going bad.  There is enough current (charge) available to start the system but not enough to get it to run continuously.  ATX system have a surge sensor and if a short is detected it shuts down the supply.  There may not actually be a short, just a faulty sensor.  Normally you an spot this as the system will attempt several time to boot and then quits attempting.

Take to a repair shop and have them try another power supply.   Do not buy one as it could be the motherboard.

Regards

[shift74]

Thank you for the reply, you put a flea in my ear when you told me about the power supply, however I can't test it properly because all the testers I have tried have 24 pin power input, while this particular power supply has 2 x 4 pin inputs, how can I test it?

[BeemerBiker]

I have the same problem with at 1600 watt mining power supply.  I put it an adapter to make it stay on so I could take some measurements for ripple or low DC, etc.  That was a month ago and it is still apart.  There is no visible damage to any components or stains on the PCB.  I pulled a couple of video boards and put in an 850 watt unit and all is back to normal.

The symptom was exactly the same:  Three spins ups of all the fans and then the system shuts down.

It may be possible to bypass the sensor test as I just read here and I will try it when I get time.

http://www.planetimming.com/atx_mod/atx_mod.html

Good Luck!