mac Pro - Screen Blank

[tonytrouble]

I have a Mac Pro - with the big mac high resolution screen attached to it. I cannot get the screen to come on. I'm 99% sure the computer bit is working . If I use the keyboard e.g. to open the cd bit and press the eject button it works. The white light in the bottom right hand corner of the screen is on and bright. The screen though is is if the computer is shut down. Any thoughts on fixing this problem would be most appreciated. Thank you.