Monitor goes into auto detect?

[Subhuman]

Hello all,I just bought a used macpro g5 dual 2.8 x 8 core computer,my monitor is a flat Dell monitor.When I first got this computer,I cut it on and everything worked great.so I shut it down and waited on my new ProTools card came in and installed it before I cut the computer back on.Now I cut the computer on and the monitor cones on but goes into auto detect mode and that's it,I scooped with the mouse and hit keys on the keyboard still nothing,so I took the monitor and hooked it back in to my older Mac and it works fine.Are there something I need to push on the new Mac to get it working correct?please help me...Thank you all...subhuman