I5 on Asus mboard - not POSTing

I've just fitted a new core i5 (socket LGA 1156) to a new asus P7P55D with a zalman heatsink; with or without RAM/VGA and disks the machine doesn't POST and the CPU_LED light remains steadily on, suggesting that the CPU is not recognised. The fans spin up but there is no sound from the speaker and (when the gfx card is connected) nothing on the display; however I don't have a second speaker to test that it is working and connected properly.

Any ideas on a course of action, is the processor or mboard dead on arrival?