Changed computer cases, now computer won't turn on

Hi all.
I moved out of a 14-year-old case (Gateway) and into an Ultra brand Gladiator mid-tower.

I have an EVGA nForce 650i Ultra Motherboard, and a "Power Up" brand 450-Watt power supply.

The setup worked fine in the old case, though Windows was freezing regularly after 15 minutes. I figured that was related to the hard-drive, since it wasn't tightly mounted, and I wasn't using enough cooling fans. So I got a new case and cannabalaized a fan from an old computer.

The power outlet and cord are good, and I swapped out the power supply with a 230 watt unit, and pulled the switch from the old case, but neither powered on the computer. Nothing seems out of the ordinary with the switch on the case I bought.

Did I buy a defective unit? Is there something I'm missing or should try again? Something else? Thanks for the help.
 
Have you considered that going from a 450 psu to only a 230 might have something to do with it?

Is the motherboard shortening out by any part of it touching the case?
 
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