I have recently built a rig with a p7p55d motherboard and an i5 750. On the motherboard there are warning lights. On attempted start-up both the CPU and RAM lights flash whilst the fans start and then it stops and repeats every two or three seconds never reaching BIOS.
The other specs are:
Coolermaster Silent Pro 700W PSU
ATI Radeon HD5770 GPU
2 x 4 GB Corsair Vengeance RAM
Coolermaster Hyper 212 + cooler
I am suspicious of a bad power supply but don't know anything else. I have checked with one stick of RAM in all the slots and then did the same with the other stick but still had the same results.
I should probably also note that I bent the com1 plug on the motherboard by accident whilst inserting the optical disk drives. I don't think I damaged anything crucial in doing so - all the connectors on it are still in place.