I don’t understand please help

[Sam38305]

Okay, so this is a household with a few computers. 
 

yesterday, my brother said his computer wasn’t connecting to his monitor or keyboard and mouse. The computer will boot and all the fans and rgb turns on. I tested it on multiple monitors and power outlets, no dice. Today I swapped out his power supply to see if that was the problem, I got the exact same situation with a different power supply so I determined it was his mobo. 
 

so since I determined it was his mobo, I was going to let him borrow my home theater pc until we fixed his. So I plugged up my home computer pc, now it will only boot for one second then it turns off. So now I have two computers that don’t work. 
 

I went and got a voltage meter, his surge protector rings out fine at 120 volts. The wall outlets rings out at 120 volts. 
 

what am I missing here? What do I need to check that I haven’t?

[ChaoticChaosx]

Check with different ram or one at a time. Also make sure the ram are in slots 2 and 4 only. On the right side from the CPU socket of traditional motherboards.

 

I had a dead ram stick and I would have no signal on monitor and keyboard and mouse unresponsive. Meaning no connection in your words.

[Sam38305]

Both computers have had different ram in them to check. But I now have two computers that are malfunctioning. Both were plugged into a surge protector that rings out fine but has somehow killed them. 

[Whatisthis]

Could be dirty power. There’s more to it than just voltage. 
 

If you moved the other computer over, I would reseat all the components first. Something like a slightly loose ram stick can make it seem dead.