No POST After Replacing Cooler

_Froyo · May 28, 2023

I recently replaced the cooler on my PC (HP EliteDesk 800 G4 TWR WS) only to find that it no longer posts. The case fan spins up to high speed for about half a minute, then spins down, then the PSU fan ramps up to full speed indefinitely, all without any error beeps / codes. I have tried re-seating the CPU, CPU cooler, and RAM, unplugging and replugging all power cables, putting the old CPU cooler back on, and clearing the CMOS, all with and without a graphics card.

Playing around with things to see what it could be, the internal buzzer did start to beep when the 4-pin CPU power cable wasn't plugged in, so the machine is still capable of giving error codes. I found that its behavior does not change when the RAM is missing altogether, so I thought maybe that was the issue. However, despite cleaning the contacts and using a working memory stick which my friend let me borrow, this didn't change anything.

My guess is that either the motherboard or PSU is the issue, but as both are proprietary HP parts, I don't know how to test them. I was wondering if anyone here had experience with this kind of situation and what you believe is going wrong here.

Specs: HP EliteDesk 800 G4 TWR WS (proprietary case, motherboard, and PSU) with i7-8700, 2x8gb DDR4-2666, Thermaltake Gravity i2 cooler, and 500gb NVMe SSD.

BushDidLewinsky · May 29, 2023

Is the backplate installed properly? - it could be causing a short in the board if not.

Robchil · May 29, 2023

On 5/28/2023 at 4:40 AM, _Froyo said:

I recently replaced the cooler on my PC (HP EliteDesk 800 G4 TWR WS) only to find that it no longer posts. The case fan spins up to high speed for about half a minute, then spins down, then the PSU fan ramps up to full speed indefinitely, all without any error beeps / codes. I have tried re-seating the CPU, CPU cooler, and RAM, unplugging and replugging all power cables, putting the old CPU cooler back on, and clearing the CMOS, all with and without a graphics card.

Playing around with things to see what it could be, the internal buzzer did start to beep when the 4-pin CPU power cable wasn't plugged in, so the machine is still capable of giving error codes. I found that its behavior does not change when the RAM is missing altogether, so I thought maybe that was the issue. However, despite cleaning the contacts and using a working memory stick which my friend let me borrow, this didn't change anything.

My guess is that either the motherboard or PSU is the issue, but as both are proprietary HP parts, I don't know how to test them. I was wondering if anyone here had experience with this kind of situation and what you believe is going wrong here.

Specs: HP EliteDesk 800 G4 TWR WS (proprietary case, motherboard, and PSU) with i7-8700, 2x8gb DDR4-2666, Thermaltake Gravity i2 cooler, and 500gb NVMe SSD.

... propretary is the worst curseword ever... what happend to the old cooler, why did you replace it? they have propretary pin outs on coolers too often. so you can't always use shelf coolers, you have to get a new one from HP. in some cases you plain fry the mainboard due to different pin outs.

the i7 8700 isn't as hot as a i7 8700k.. but is still a prime candidate for deliding if it's a heating issue.. on a 8700k it would drop the temp with up to 20C due to crap compond inside. but it is soft, and easy to remove when delidding.