Every time an issue like this arises and nothing seems to work, it's recommended to try and run everything outside the case. the PSU and drives can stay, but the motherboard should come out. This eliminates the possibility of any shorts.
If the case power switch connector doesn't reach, you can still turn it on by momentarily shorting the power pins on the motherboard (where the cable was connected). I use a metal tipped pen.
I know it sounds silly, but you'd be surprised how many times it has worked. For myself, and many on here as well.
If that doesn't work, I'd re-seat the processor and heatsink, as well as re-plug all the cables. Make sure that the 4-pin/8-pin power cable is plugged into the motherboard as well.
Also, see if you can try a different power supply. That would be my first guess if we were to rule out components.
Good luck, and be back in the morning. Edited by Shift. - 10/26/11 at 11:07pm