THESE MAY SOUND STUPID BUT WORTH A SHOT ... WORKED FOR ME
try tightening all the connectors.
Remove the RAM and Rub the Pins of the RAM with an eraser
Try to unplug all the devices including mouse and keyboard. (Sometimes due to a component PC fails to boot due to faulty component)
Just connect the Monitor and try to turn on the Pc
and can u tell more about the problem?