My company has that Nortel Norstar Startalk Flash system. One of the mailbox extensions in now functioning like a guest mailbox. External calls go directly to voicemail and the he phone does not ring. The display does not show there are messages on the second line of the display. If another extension tries to call it using Intercom, you hear a busy signal and the display reads Not in Service. When Function 981 is pressed, the display reads Log: and you have to enter the extension and the password. How can I fix this problem and change the phone back to a personal mailbox?