Ok, first of all, make sure the computer is ON. Then depending on what type of connection method u r using, set it on that. For example, if using DVI, set your monitor on that number to accept the signal. Usually a button on ur monitor that will let you change inputs.
Hope this helps.
Good stuff Roshan, you will soon become as much of a nerd as me.
Kraut, I assume that you have a higher-end video card. If this is the case make sure you have power getting to the bad boy. This is to say that you will most likely have a slot on your card to hook up your power supply to your card (i.e. Molex connector). Without power the card will not be able to display anything.
If this still doesn't work try reseting your BIOS. You will have to look over your motherboards documentation to see which jumper to remove to be able to reset it. Or you can do it the quick and dirty way by removing your CMOS battery, turning on the system and leaving it on for a minute or so, shut the system down, put the battery back in and start the system up again.
There is also the issue of your BIOS settings if you get it reset...
Does your motherboard have onboard video? If so you will need to disable it before you will be able to use a PCI-X or AGP card.
Troubleshootin
g is fun!