If you're installing and removing the video card with the system powered up, then it's strongly recommended that you refrain from doing that.
Install/connect only the power supply, MB, CPU, memory, video card, monitor, keyboard, 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 a display, then install all other components one at a time until the problem resurfaces. The last component installed, its slot, its MB connector, or its cable is the culprit.
If there's no display, then clear CMOS with a MB jumper, or by removing the CMOS battery for at least 30 minutes.
If that's already been done, then make sure the 'Clear CMOS' MB jumper is not in the 'Clear' position.
If the jumper is in the proper position, then check the CMOS battery for the correct voltage(3V).
If no luck, 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 none is found, then remove all MB screws and metal standoffs, and install paper washers(manila folder paper works good for this) 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 described here:
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 install the memory modules one at a time in different slots, 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.