My mac mini won't start

Hello!

I have a 2011 Mac mini that won't start anymore. It powers on and the apple logo and the progress bar shows up. When the progress bar reaches the middle, the screen goes black, then comes back grey again, but with a fine vertical moiré pattern. Then 10 seconds later it powers itself off and tries to start again.

I tried starting in all possible modes, all with the same result. The hardware test cannot find any faults. I'm including the Verbose log here, if that helps someone.

It has ifixit's dual hard drive kit with a SSD as main disk and has been running like that for years. I just tried replacing it with another HDD, but same results. Also tried with another set of RAM, but no difference there either.

I'm guessing some sort of hardware defect, but what? Anyone has an idea?