Computer has power but nothing else!!!

My computer will no longer boot. The system has power, fans move, light up but nothing else...Also, cannot shut down system from front of case. I have tried to remove all non-critical parts, reboot and get sounds but still no beeps or anything...any suggestions? Most internal hardware is non-refundable at stores so I cannot "try" hardware to fix the system...what to do?

CPU: That's pretty rare
RAM: Same
HDD: Same
Power Supply: Maybe, but then you have power which means if there's a possibility of PSU problem at all, its a intermittent problem. But, usually the whole PSU fails. You can check it out though.
Mainboard: Weird, but most problems point towards the motherboard. I think the reason is there is just too many point of failure due to the sheer amount of components.

First thing I'll do is see if your store can do anything about it, unless you have bought it from multiple stores.