Question turning off and on suddenly

[parsi]

hello to friends.

i bought a whole pc recently and i have a serious problem which i couldnt find any solution for it until now.

my pc turn off suddenly without no error and crash or even freezing then after 2 or 3 second it turn on again and still doesnt show any error or bug....

this problem occur suddenly :for example three time in 2 hour and another time it happen after 3 or 4 days later for one time!
i have to notice that this problem is different as restart because when it happen all front panel lights would shut down in while its off
i found a way that i can make this problem intentionally : when i enter the uefi(bios) and want to update my mb bios, it give a notice that says "pc will restart in 5 minute then bois will install" but after this countdown,
pc would turns off as i said !!!!!
i tried many way that are in all sites also motherboard warranty service gave me another motherboard as same as previous one but i think its because of another thing . my pc specification:
my cpu temp is always below 48 degree

cpu:core i5 8400
ram: 8 gig team group tforce 2666
mother board: asus prime b365m-a
power supply:cooler master 550w
graphic: intel gpu integrate
cpu fan: deep cool gammax 200
thank you for your answer

 

[ChumP]

If it's like a sudden power loss when it happens, I'd suspect the PSU as being the main candidate.

You pointed out that you RMA'd the motherboard aswell, so the next thing to test is the PSU.
The only way to test this unfortunately is changing it with another working unit.

 

[parsi]

If it's like a sudden power loss when it happens, I'd suspect the PSU as being the main candidate.

You pointed out that you RMA'd the motherboard aswell, so the next thing to test is the PSU.
The only way to test this unfortunately is changing it with another working unit.

Yes its sudden, actually i changed my psu with another one but the problem doesn't solve, I don't know any other way😪😪 to do