Msi Z270 Sli Plus Motherboard

I have the MSI z 270 Plus Motherboard with the Pentium i5 cpu. All the drivers are fine. I am having a weird booting issue.

I can reboot, and computer starts fine, If the computer sits for a hour or more, it wont boot up, Everything starts up fine, but the bios wont show up.

If I turn the power off using the switch behind the tower, then turn it back on, then fire up the computer works as it should. Does this 99 percent of the time. Once after sitting quite awhile, computer booted up as it should.

 

Possible overheating -

 

Oh, what I should of said, when it sits, its shut off.

 

Sorry, I have not been about for a few days- I did think someone else might have come in, whilst I was away, but this virus thing could be making things difficult .
If it is overheating, you have to look at several things.
If you look inside , the cooling system needs to be clean-fluff and hair, and dust can collect in the cpu fan, and cooler- an internal fan may not be functioning.
If it stays on long enough ,go to EVENT VIEWER, and see if any warnings are there- critical, or,y ellow triangles.
If in Windows 10, right click the start button,on bottom left of screen, and then left click EVENT VIEWER
Come back with the result