DL380 G9 won't start after turning it off

[Nicolas2]

I've got 2 new DL380 G9 servers and both of them won't start after having turned them off for a couple of hours. The power button light is inactive instead of being amber.  Pressing it does nothing.

A way around this is to disconnect the power for around 5 seconds. But it's obvious that this isn't a real solution though. I've googled the issue and found nothing. 

Because both of them have it I figure this is a setting that I should alter, I have no clue which one though...

Is this a known issue? If so, how do I solve it?

EDIT: the light being off means that the server thinks there is no power present, which can't be true because on the back the light indicator for the power cable is solid green.