Will the MWL light on that phone at all?
Switch it to a port that you know has a working MWL and leave a message.
Or call that extension and while it's ringing press the message waiting button on the phone your calling from and see if that MWL lights.

To assign ringing to another extension go into 408-409 & 410
If anything is assigned in 414, 415 or 416 make sure nothing is set as DIL 1-1
If it is change it to normal.
Gem