Changing output res blind

Hi

I have acquired a 2006 mac pro running Lion and am trying to display it on a VGA only monitor (using DVI VGA adapter). I see the boot up screen then when the desktop should appear the monitor goes black and tells me there is no input. The previous owner had apple cinema displays so I imagine that the output is set too high. Will zapping the pram change the screen res? I don't have any other monitor to try.

Thanks

Phil.

Do you have a TV with HDMI inputs?
If so, you can use a DVI to HDMI adapter and use the TV to access settings.

Afraid not :-(