HP won't boot

Hey ya' all........
My niece son asked me to fix this computer.......been a while but I believe it is the mobo /or cpu...........can anyone help me to determine this ?
I hooked up a working psu.......fans kick on for a second and stop.....
without my psu .......nothing would work....
Thanx for any thoughts....
TW

What is the make and model of that pc?

Thanx Train for your reply.......managed to get it to boot........the psu was the culpret........
Have a great day........

Glad to see the good news!