|An operational motherboard is required for power to come up completely. The motherboard 'might' have been damaged by the power surge. |
There is also the possibility that a defective unit connected to the motherboard could be preventing the motherboard from operating properly. Disconnecting everything (except the front panel wires) from the motherboard should eliminate that possibility.
As a last resort, pull the RAM sticks. If you get error beeps, that would tend to indicate that the motherboard is ok, but there is a RAM problem.