If you tested the screen and it works then you should check your video card.
What kind do you have: PCI-E/AGP Integrated or both (Integrated + PCI-E/AGP)
Try switching your addon card with a known good working one or try it in another conputer.
If you have an addon card and the option of Integrated video and want to try the integrated make sure to take out the addon card before trying it.
If you tried your addon card in another computer and it works but it does not work in your computer it may mean a faulty PCI-E/AGP slot but could also mean a faulty PSU (Power Supply) not able to send enough power to initialize your Addon video card.
Motherboard model or computer model (like Dell... HP... ect) would help for any further assistance
Hope that helps
Edited by Alzeimer, 05 July 2012 - 09:52 PM.