BIOSTAR N4SLI-A9 Won't Power Up

My sons friend bought a biostar n4sli-a9 along with a new case, cpu,
mem and vid card. He physically put everything together and has been
unable to get it to power up. He's asked me for help and I'm stuck.
Here's the details.

The case he bought had the wrong power supply, 20 pin instead of 24.
I know he tried to power it up at least once. I tend to doubt this
fried anything, but you never know

He got a correct 24 pin (plus 4 pin aux) power supply and put that in
with no luck. No fans no lights, nothing. The power supply fan does
not come on at all.

He brought it to me for help. I unplugged everything and inspected
his connections. He attached the mobo to the case using 4 screws with
insulators on the top but nothing on the bottom. This meant that the
mobo had no standoffs from the bottom of the case. The edge away from
the back of the case was definitely flexing, but not too much really.
I doubt this was enough to physically crack the board but it's possible
that he may have been grounding out something on the bottom.

I took the mobo completely out of the case, connected the 24 main power
and the 4 pin aux power, and plugged in the power supply....nothing.
I also unplugged the mobo and ran the power supply totally
bare.....nothing!!

Did he fry a brand new 400 watt PS *and* his mobo?? This seems
unlikely, but how can I troubleshoot this??

Thanks for any help. This was the kids man xmas present this year and
he's really bummed out!!

Gary