|It could be that the video has failed, but the computer is|
working correctly, or the computer itself may have failed.
Plugging in another monitor, as Johnw suggested, is one
good way to test to determine which it is. Another way is
to listen for the sounds of a normal boot up. If you hear all
the normal sounds but nothing ever appears on the screen,
then you can be pretty sure the problem is either in the video
controller, the monitor, or the connection between them.
Probably the first thing to check is that the monitor is set
correctly. I once turned the brightness all the way down on
my monitor before turning the computer off. When I turned
it back on, I forgot that I had changed the brightness, and
thought the monitor had died.
-- Jeff, in Minneapolis