My guess would be that the Power Supply took a major hit after that power outage. The damage didn't happen when the power went out, it happened when the power went back on. Surge Protectors are helpful in that type of situation. They can minimize the amount of amperage that is dumped back into the PSU when the power returns.
Even a damaged PSU can provide a small amount of voltage to power the Motherboard light. But not nearly enough to start the boot process and power all components.
I bet if you swap out your power supply with a new one, you're problem will be solved.
There is really only one company that you can get a PSU for a Dell 4600. www.pcpowerandcooling.com