i9 9900k stuck at 800Mhz, no progress for days.

[SWith3]

I have a newly built system here with an i9 9900k and as ASUS TUF Z390 Pro-Gaming motherboard that is stuck at 800 Mhz. It's a fresh and fully updated version of windows 10 ultimate.

I have tried the following:

1. Took off cooling unit (Corsair H75 liquid cooler) cleaned and applied new Arctic MX-2 thermal paste and made sure the cooler was snug but not tight.

2. Set windows power settings to max performance

3. Reset BIOS to default. Only changes I make are making sure it's set to AHCI and XMP memory profile.

4. Reset CMOS

5. Different benchmark/stress methods.

6. Double checked all connections and fans.

7. ASUS tech support (no help)

8. Windows Safe Mode

9. Intel Processor Test Tool, all passes.

10. I don't think there is a slow boot option on this board, which I have read about but don't much about.

 All the cores sit at 800Mhz and do not increase even during games or CPU benchmarking. Temps don't do much more than 33c. The multiplier stays at 8x and it sits around 0.639v.

I have no idea what else to do. I'm not even sure if the issue is the board or the CPU. What would force the CPU to be throttled down to minimum?

Any help would be greatly appreciated.

[SWith3]

I took everything apart and put it back together again and there are no more problems. My best guess is the CPU was ever so slightly not fully seated. Enough to work, just not properly.

[GreenMan]

I had the very same issue and in my case was able to solve it. Premise: I do use a Corsair AIO (which was the culprit). I will spare you the details of how I got here, but this is the issue.

When tightening the AIO pump to the CPU, as I did on the same machine with the previous CPU's I had installed, on this particular case, the pressure was too much. 

So, my solution was to tighten the AIO pump as little as possible while still maintaining a sufficient thermal conductivity between the CPU and the cooler plate.

Now all is peachy.