Call Pilot is Inactive

Check in Maintenance/Port Status to see if the KSU see's the Call Pilot.
Check/Replace the mod cords
Check pins in RJ11 (both CP and Jack) have not jumped out of grooves.
Check/Replace Cross Connect wire
Check/Replace Power Supply (see below)
Check/Replace BIX or 66 Block
Check boot sequence using Hyper Terminal (see far below)
If on network and there was changes to the network IP's or to the Call Pilot then unplug the network cable, change the IP and subnet and gateways via laptop to the defaults and reboot.

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Early model Power Supply cords with 3 prongs (9 volts) have been failing (and recalled) and are to be replaced by 2 prong (8 volts) cords.
Symptoms with the PS are:
PS has slight swelling
PS is hot to touch
PS is stone cold

If it is luke warm:
Note that also the voltage may be present to light up the lighs but not correct enough to boot up the Call Pilot.

It is suggested you replace the 3 prong cords anyway with new 2 prong cords soon as possible to avoid failure.

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Hooking up a laptop and using hyper terminal can help in troubleshooting issues by reading the boot sequence.
If you notice it keeps rebooting then it might be because of the PS issue, IP address is wrong or does not match the current network if plugged into a switch/hub.
See first part of this thread to use Hyper Terminal:
http://www.tek-tips.com/faqs.cfm?fid=5226