When you call the VM in-house, does it actually answer?
No, the LEDs won't turn green. They should be lit steadily when the ports are idle, and flash whenever one of them is in use. If anything else is happening with them, then the VM is in trouble.
My suspicion would be that the SLT adapter (7420) may be the culprit, which is a very good thing. Obviously, the Dispatch is functional meaning that the hard drive is still good (that's usually what fails on them).
You'll need to connect a true single line telephone set to all of the SLT adapter's ports and try ringing each one by dialing their respective extension numbers. If you don't ring the phone, then the 7420 has failed. Check back and let us know.
