Question Motherboard does not turn on most of the time ?

[cbsn]

My motherboard turns on randomly, but most of the time it does not turn on.
Background : My old mobo was not turning on, it seemed that the PCH was shorted. I bought a new mobo as well as a new PSU, and the problem seemed gone, as it was working great outside the case, I even used the computer for awhile. Then, I put everything in the case, turned it on, but, the pc turned off at the middle of the boot, and did not want to turn on anymore. I took everything out, tested again, but no success. Then, by testing, I realized that if I wait sometime, about 10 minutes with the PSU off, it starts working again. But, if I plug another cable or try to do anything it wont start anymore, I would have to wait the same time for it to work. Does anyone have any hints? Thanks in advance!

Mobo : msi mortar b360m
PSU: Corsair cx750m

 

[Lutfij]

PSU: Corsair cx750m
Is this the grey labelled CX unit of the green labelled CX unit?

When posting a thread of troubleshooting nature, it's customary to include your full system's specs. Please list the specs to your build like so:
CPU:
CPU cooler:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
Chassis:
OS:
Monitor:
include the age of the PSU apart from it's make and model. BIOS version for your motherboard at this moment of time.

To also add, you breadboard the entire system to verify that the case isn't causing a short to prevent the build from powering up/POST'ing.

Relocate to another wall outlet and see if the issue persists.

 

[cbsn]

PSU: Corsair cx750m
Is this the grey labelled CX unit of the green labelled CX unit?

When posting a thread of troubleshooting nature, it's customary to include your full system's specs. Please list the specs to your build like so:
CPU:
CPU cooler:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
Chassis:
OS:
Monitor:
include the age of the PSU apart from it's make and model. BIOS version for your motherboard at this moment of time.

To also add, you breadboard the entire system to verify that the case isn't causing a short to prevent the build from powering up/POST'ing.

Relocate to another wall outlet and see if the issue persists.

CPU: i5 9400f
CPU cooler: Intel Standard
Motherboard: msi b360m mortar
Ram: 2x8gb 2666mhz hyperx
SSD/HDD: HDD Sata Standard
GPU: gtx 1660 ti
PSU: corsair cxt750m, semi-modular, grey color
OS: win10
Monitor: AOC sniper 75hz

PSU is brand new.. I tried with my old one and it also does not work. I have a multimeter to measure if I have to, I just do not know what to.
I should also mention that when I took it off I have seen some thermal paste (size of a rice) in the lower part of the mobo, to be more precise, in the hd audio connector. I do not know if it was the problem, but I cannot see anything else I could have done wrong as I have had this problem before and I usually take every care I can to prevent it.

 

[cbsn]

PSU: Corsair cx750m
Is this the grey labelled CX unit of the green labelled CX unit?

When posting a thread of troubleshooting nature, it's customary to include your full system's specs. Please list the specs to your build like so:
CPU:
CPU cooler:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
Chassis:
OS:
Monitor:
include the age of the PSU apart from it's make and model. BIOS version for your motherboard at this moment of time.

To also add, you breadboard the entire system to verify that the case isn't causing a short to prevent the build from powering up/POST'ing.

Relocate to another wall outlet and see if the issue persists.

Update :The mobo has debug leds... One for CPU, one for DRAM, one for BOOT and one for VGA. As I said, if I wait sometime then it will eventually turn on, but then off within some seconds. Between this time, it checks the ram and the cpu, only keeps waiting for the vga until it turns off. I decided to plug the GPU to see if I could get any video before it turns off, and.. it did not turn off anymore.. It is werid because I did the same thing, ie, turned it on with a single ram stick and the cpu and it did not turn off like it did. I know it may have a faulty thing on the mobo, but I hope it keeps working!