It;s gotta be PSU or mobo fault. I'm picking PSU because absolutely nothing happens when switched on. A very outside possibility is the power on switch( i've only ever seen this once). You try this as a very last attempt before looking at finding a psu. You should be able to trace this to the front panel header for switch, reset, power\hd led etc.. It is will have something like pwrsw next to it. http://www.computerhope.com/jargon/s/systempanel.jpg
Try shorting the pwr and ground pin which has the same effect as the mechanical switch on case.
Thats about all i can suggest as of now.