Is your system dead with no power LEDs on the PSU?
Is your cabinet emmiting a loud buzzing chattering sound?
Do you have loud humming on analog extensions & CO lines?
Is your PSU missing one voltage +5, -5, +30 or -48?
Is the red BATT LED lit up and only a single cabinet (can be on blinking with chattering sound)?
If so you need a PSU repair.