Hi jango,
I will reply more indepth tomorrow, but just wanted to say that according to
THIS LIST your Mac has ADB and DVI, and includes DVI to VGA adapter.
So, you can attach any monitor that has DVI directly with a DVI lead, and any monitor that has VGA with the DVI to VGA adapter. The ADB port you are currently using (I assume) will not be needed if you go for a non-Apple monitor.
Have you installed any new memory in the machine lately? The quickest way to rule out the monitor is to attach is to another computer (borrow one if you have to, but make sure you use the right lead/adapter for another system

)