Follow the steps below and see if this fixes the issue:
1. Try to reseat the monitor cables (both power and data cables).
2. If you don't get video in the above step, try this monitor with a different computer (if possible a friend's computer).
3. If the monitor can't display any video on the other computer as well the problem might be with the monitor itself. Do get in touch with the monitor's manufacturer or their website for model specific settings/troubleshooting.
4. Try a different monitor (if possible) with your computer. If the video is good on this monitor, this symptom also indicates some problem with the original monitor.
5. If the monitor works fine with other computer, check the monitor settings and the input mode (such as, VGA, DVI, HDMI, etc.). If you don't get video after changing the settings, try to reseat the video card (if any) in the machine. (Note: open the chassis and work inside the machine only if you are comfortable otherwise it is advisable to seek technician's help also ensure that all the power connections and other devices are disconnected before you open the chassis).
If any of the above steps don't fix the problem, do reply with the Monitor's make (model), the Graphics Card and Operating System and also any hardware/software changes you made recently to the computer.
