Make sure that the monitor is plugged in and turned on. Check for a power indicator on the front of the monitor, it's normally a green LED.
Check the connection between the video card and monitor. Make sure the cable is connected securely on both ends and is not loose or has broken pins.
Make sure that the PC is on and running. LED's should be lit on the front of the PC's case and you should hear sound coming from the inside the PC.
Your video card may not be producing any output. Try connecting the monitor to another PC if possible. If it works on the second PC, the monitor is OK.
Remove the cover from the case after you have disconnected the Power cord and Monitor cable from the PC and ground yourself by placing the back of your hand on the Power Supply Unit and not moving your feet. By not taking this precaution it is possible that you could inadvertantly cause damage to the PC from an electrostatic discharge.
Make sure that the video card is tightly and completely inserted into its slot. Try removing and reinserting the Video card and then rebooting. If the screen is still the same replace the Video card if the Monitor has checked out OK.
If it is a Notebook try connecting to an external Monitor. If you have a display on the external monitor you have a problem with the LCD screen and you will have to take it to a qualified Technician to have it serviced. Try removing and reinserting the cable from the Video card to the LCD Monitor. They have been known to creep.
If there is no display on the external Monitor it would mean theat the Video card has gone to Silicone Heaven along with the Motherboard.
