Computer shuts off after a split second

[lil barack]

Hey, my dad's computer had this issue where his comp would turn off and on repeatedly. So I took out his old psu and put in a new one and now I'm getting this issue where it shuts off a split second after I switch on the psu and power button. Is there something I could have missed when installing the new psu? I haven't had any installing problems like this with any other computers I've used. Is the motherboard shorted and how can I tell?

[The_Dillster]

By the sounds of it, it's not the psu. I'd think it was the mobo but i'd still do  a memtest86 just to be safe even if it doesn't bluescreen

[lil barack]

By the sounds of it, it's not the psu. I'd think it was the mobo but i'd still do a memtest86 just to be safe even if it doesn't bluescreen

For ram? I checked the 3 ram sticks seperately and all have yhe same effect, also this was my old psu so it could only be cpu/mobo that would be the problem