I think you said the display powers up. So you get the GeForce card's own display first, then the Mobo's bits about the BIOS, memory installed, etc - yes?
It then sees three SATA devices - hard drive and two DVD burners - yes?
So something's working, then it gets the hump.
Will it boot from a CD or a DVD in one of those DVD burners? Do you have a Knoppix CD (always a useful thing to have lying around)? Will it boot that?
Since we've eliminated the absence of heatsink paste, try SD's suggestion - remove all but the graphics card and one stick of memory (so no drives). See if that does the same.
Do you have another graphics card lying conveniently around? Anything would do, even an old PCI one - anything that will fit.
Graphics cards get very hot, and if there's something wrong with one, it can pull large amounts of current so that the voltage available drops too low for other bits to run.