Replaced right hinge clutch, computer won't startup

Okay. I'm no noob at these kinds of repairs. I followed the excellent guide at this site for the repair and easily kept track of all screws, didn't break any tabs or connectors, etc. But now that the computer is back together, it won't start up. The optical drive receives power, the hard drive spins up, and that's it. No startup sound. Nothing on the LCD. No backlight. I even took the keyboard off to double check that all internal connections were correct and intact. I even attempted to reset the power management, just in case that would magically fix something, but heard no startup sounds to indicate it worked.

The only thing I can think of is that this is my wife's computer, and she hasn't exactly been gentle with it. Lots of damage to the external case. Could it be that opening it up exacerbated a preexisting crack in the motherboard or something? It's just that the internals looked okay, and I can't detect anything I might have done to cause this! Let me know what you think. Any help is greatly appreciated!