At this time based on what you have told me if I had to guess I would go with the motherboard, which part of the motherboard would be hard to say, if the hard drives were spinning up and running the OS, which could be seen by watching a lot of led activity, then stopping at the "welcome" screen then more activity as it loads the GUI, then very little activity from then, then if that happens the southbridge and hard drives are good. If you have shotgunned the processor and no change then odds are that the processor is not the issue. RAM can and will stop a boot, and if your system was overclocked, there is a possibility that the RAM has gone bad, if you have tried other RAM and the issue continues, then you are down to then mobo again, without integrated video, a thought would be the northbridge, again if the system was overclocked its possible it was damaged by heat and over voltage.If it was then a hair dryer won't be able to fix it. There is a possibility that the PSU has dropped a leg, a distinct possibility would be the CPU power leg, again not that unheard of, the symptoms you posted would make me think it is in the socket northbridge area, which would include the CPU power plug. If you have a volt meter check the voltage output on the cpu plug, if it is there then again it would point back to the northbridge.
I know this seems painful, but believe it or not, troubleshooting a computer system that you can see if rough, there are so many things to watch when you press the power switch, the fans, the hdd led, etc. But trying to help as best as I can under these circumstances. You never did reply about Hiren's?
