Won't post or boot 2nd time.

[Tripl37s]

So I am having issues with a PC I just built. The issue with the PC will not post. If I remove the CPU and put it back it will post and boot . However after that if it's left on for more than 2 hours it will shut off on its own.  If I try to turn it on it won't even start the post process just the stand by led.  1 time it tried to post and the post led was red which is a cpu issues on mobo. I guess my confusion is I have access to 3 CPU all of which will post and start the 1st time I place them in the mobo so I am guessing the issues isn't the CPU it self .  I am guessing the issues must be mobo related but I wanted to ask for some help here 1st before I go sending parts back . I have also re seated all the other parts.  I also set the ram from xmp back to the default just in case that was the issue

Parts 

Ryzen 3600/3700x / athlon 220ge
Asus b450i strix 
2060 ko ultra 
Lpx 16gb 3200

Thank you for any and all input

[Prathamesh232]

three cpus did the same?

it may be the motherboard then, 

you're running a good psu right?

 

[Tripl37s]

1 minute ago, Prathamesh232 said:

three cpus did the same?

it may be the motherboard then, 

you're running a good psu right?

 

Yes it's a Corsair sfx unit. I may be able to borrow a PSU from a friend just to rule that out . I was hoping it wasn't the mobo since it's pretty much out of stock everywhere and the back order for it is crazy once it's actually in stock 

[Chabax]

bro are you repasting paste every time when replacing CPU or removing heatsink from CPU? cuz every time u move CPU heatsink it will create air bubbles whic will make hotspots on ur CPU and overheat it, clean paste completely every time use alcohol wipes or something

[Tripl37s]

4 minutes ago, Chabax said:

bro are you repasting paste every time when replacing CPU or removing heatsink from CPU? cuz every time u move CPU heatsink it will create air bubbles whic will make hotspots on ur CPU and overheat it, clean paste completely every time use alcohol wipes or something

Yes I've repasted every time and have been cleaning it with the noctua  wipes . Someone on reddit suggested I take a look into my vrm temps so I have it back on now and alll the temps look good if it shuts off again I am going to switch for the l12s to the stock cooler just to see if that changes anything