Why won't my computer boot?

Question

I have bought an 'ordinary' Asus P5E3 motherboard and an Intel Q9450 Quad core processor. But there is no POST when we turn on the compuetr - that is: the monitor stays blank although all the fans turn and motherboard LED lights up. We have put 2GB of DDR3 Ocz 1333MHz memory in all configurations and-nothing! We tried the memory in a Gigabyte board and it's fine. Then we tried the processor in the Gigabyte board and it would not POST. The graphics card is a Gigabyte PCIe x16 but there are no signs of rejection. Is it possible that I need DDR3 Graphics card? or is the processor faulty?