you should check the power supply, try another good PS, check the litiumbat on the motherboard. As a final attempt, remove everything from the case, examine every part looking for faulty symptoms. Put all the parts together, doublecheck all connection for poorly fitted cables. There is always a possibility to set-up the computer-parts outside the case - just in case to check whether you have a "short" inside the case.
Press the power-on button, if you are lucky - or done a good job - then you will be back in business
Cheers
IB
