Most problems like this are due to motherboards not being mounted properly did the case have brass standoffs or did it have raised mounts already there?.
If you don't have raised mounts and mounted to back plane its shorting out the power supply or if you have brass standoffs you may have one in a spot where there is no mounting hole shorting out the power supply.http://www.personal.psu.edu/students/r/q/rql5024/published/STEP-BY-STEP-PROCEDURE_1.html
1) remove the motherboard from case and the power supply put the motherboard on a flat clean non-conductive surface and plug the power supply in.
2) try resetting the bios by using jumper or remove the battery for 10 mins and put it back in.
3) plug in the video if it has onboard or insert a pci-e video card and plug into monitor.
4) look in manual locate front panel connector power lead and short with small flat screwdriver on front panel on motherboard.
5) if it powers up and runs look at the back plane in case make sure no brass standoffs are where there are no mount holes on motherboard.