Intermittent no POST

[MrChalky]

Specs:

• AMD Ryzen 5 5600X
• MSI MAG B550 TOMAHAWK
• Corsair Vengeance RGB PRO 32GB (2 x 16GB) DDR4 3600MHz C18
• Corsair RM850x
• NVIDIA GeForce GTX 970

 

Every single time I try to boot, the first time it doesn't post. some rgb lights turn on, but there's no one home.

I press the power button again (short press) - it shuts off, and when I try again it boots fine.

Even if the computer has been on for a while, if I shut it off, and try to boot up again straight away I get the same issue.

Always fails the first time, always works the second.

 

I've reseated everything, checked all power cables. PSU is new enough, but it was working fine in a previous build.

[MrChalky]

When it doesn't boot, VGA debug light remains lit