if you plug it back into your first pc...Does it work?
Do you have the improved version Xenarc or the old version.
The older version have a really weak connector...I know mines snapped of and so do others that had the first version.
Did you try cycling through the different displays?
Does your PC works with the monitor unplug then plug? Try plugging everything in first, then turn on your PC.
The Xenarc will always turn on by itself once it detected a signal. No need to press the power button at all