Wondering why I had this problem

[bingotj1]

So everything is fine now, but curiosity has been killing me on why I was having this issue. In 2012 I built my first PC and I put everything together correctly and when I tried to turn it on literally nothing happened so I threw it aside for a few years and then in 2014 I got to working on it and I breadboarded it and it worked outside of the case so I put it back in and it didn't turn on so I breadboarded it again and it was working again. So what I did was installed the components in my case while powered on (it was a desperate attempt) and I discovered that I could only have 2 screws holding my motherboard into my case. The positions of the screws were irrelevant but if I had more than two it would power off. What could be the reason?

 

[Flying Head]

Screw heads too big?

 

[BadActor]

Were you using standoffs in all the correct holes and no extras? I have also seen rivets stick up too high and touch the back of the motherboard.

 

[little_me]

Things in order of likelihood:
-one of the stand-offs is likely in wrong place and caused shortcircuit which in turn turned PSU off as a safety feature.
-One of the backplate shield i/O panel grounding flaps (USB ports and such) might be bent wrong and touching wrong part of the port/motherboard, causing the shortcircuit.
-some other reason I can't think of right now. The symptom of turning off pretty much describes power supply shortcircuit protection, for which the reason pretty much always is.. shortcircuit.

and yes, it is better to shut off than burn whole computer/PSU, whichever happens first.