After switching motherboards, PC doesn't boot; PSU light just dies instantly

[hookonsonic2]

So an older computer of mine got affected by a lightning storm and, after some deductive reasoning, I concluded that the motherboard needed to be changed. I got a new motherboard today (2, in fact, due to an error), and switched out all of the cords (or so I think). After I got everything put back together, I plugged it in. With the old motherboard, the PSU light would just blink a few times per second, but now it just stays steady like it should. I proceeded to hit the power button, and before anything even happens, the PSU light just turns off. No fans, no beeps, absolutely nothing. The lights in my room flicker for but a moment, so there's power going in at some point. Does this sound like a motherboard or PSU problem to you guys?

This was my first motherboard change that I've ever done, so I'm worried that I put something in the wrong spot or maybe even forgot something. I'd also really hate it if it was just the PSU that was broken and not the motherboard. Any help would be appreciated.

Specs: Compaq Presario SR2012NX
New mobo: ASRock A785GM-LE
CPU: Original AMD Sempron 3400+
RAM: Original DDR2 SDRAM PC2-4200 240-pin 256MBx2
GPU: Integrated ATI Radeon HD 4200

It might help to tell you guys that I moved the CPU while it still had thermal grease, so I pulled it out as gently as possible with some pliers. I didn't notice any damage of any sort, but I'm wondering if just that tiny little squeeze could've hurt anything. Is there a chance that I got some thermal grease on something? Would that cause the PC to not boot? Again, any help would be appreciated.

 

[cl-scott]

Assuming the PSU was present during the lightning storm, then I would absolutely replace that first and see how things go from there. Unless the surge came over like an ethernet cable or something of that sort, the PSU is the obvious gateway to the rest of the system. If something inside the unit was damaged, then it would stand to reason the PSU could easily have been damaged.

 

[hookonsonic2]

I fixed the problem. The PSU was NOT the problem, however. Trust me, I tested it pretty well. I had hooked another computer's motherboard to the broken computer's PSU and the light on the PSU was good and steady. I made a dumb mistake, however, when I was plugging in all the cords. In retrospect, I should've looked at the wiring guide that the mobo came with. I plugged some 4-prong power cord into a place that it definitely shouldn't have been in, which was causing an instant short in the computer. It's working fine now, and the mobo was all I needed to replace.

This is a lesson for all people doing their first motherboard replacement: Look at the instructions and write down or take pictures of where the wires originally were. Write down which wires are and aren't plugged in. It'll save you a lot of potential hassle down the road.