Either try a different monitor on your system, or connect yours to another system.
If a different monitor works on your system, or your monitor does not work on another system, then replace your monitor.
If your monitor tests ok, then install/connect only the power supply, MB, CPU, memory, video card, monitor, case speaker, and power button, and make sure the power supply's voltage selector switch is set to the correct voltage and the PS connection to the MB is securely seated.
If there's no display, then check the CMOS battery for the correct voltage(3V).
If that's ok, then make sure the 'Clear CMOS' MB jumper is not in the 'Clear' position.
If no luck with the above, then place the MB on a piece of cardboard.
If there's now a display, then the MB is shorting out when installed in the case. Check for a loose screw, standoff, etc., inside the case, and also remove any standoffs which do not line up with MB holes.
If no luck, then remove all MB screws and metal standoffs, and install paper washers(a manila folder makes good ones) between the MB and the screws/standoffs.
If there's no display with the MB placed on a piece of cardboard, then proceed with the following:
1- If all fans and lights work when the 'Power On' button is pushed, then test the PS as shown here:
If the voltages are not up to spec, then the PS is bad.
If you do not have a voltmeter, then try a different PS.
2- If the PS voltages are ok, or there's no display with a different PS, then either the MB, CPU, memory, or video card may be bad.
Make sure the correct memory type is being used, remove and reinsert the memory a few times making sure it's firmly seated, install the memory in different slots(some MB's require that their memory slots be populated starting with slot 4 and not slot 1), and make sure the video card is firmly seated(some video cards need an extra firm push to seat properly).
If still no display, then swap out the MB, CPU, memory, and video card to find out which one is defective.
