Ok, stupid one out of the way first - Is the monitor connected & plugged in? :smileyhappy:

Have you tried swapping the graphics card for another one from a machine you know works? 

More info would be good, was it working to begin with or have you just bought it and it doesn't work?

i checked everything vga card is working properly and everything is pluged in wright way .

What you're not telling us is what kind of monitor is it, CRT or LCD?  Is the monitor on before you start the computer or do both come on at once.  How long until you see something on the screen?  Any other error messages or problems?  Does the same thing happen with another monitor (if tried) Details, details!