Mac Pro wont recognize Apple monitor

Hi,
I run dual monitors with my Mac Pro (first intel version)
I have a samsung and an old apple monitor.
It worked fine until I disconnected everything to fix the tangled cord issue.

I put it back together and the apple monitor is recognized but the screen is black. (yes, I double-checked to make sure it's on.)

I know the mouse travels to the black screen because I opened a finder window which did not show up on the samsung screen and after some 'fishing' I was able to drag it from the black screen to the samsung screen.

The old apple monitor uses the VGA port.
Any help is appreciated.

just swirched inputs

I just switched the monitor inputs in the back of the Mac Pro.
The samsung still works t he apple monitor is detected, but still black. The button on the front of the apple monitor in bottom right is lit up, however when I press on the sun looking emblem on the lower left there is no response.