We installed 16 M3905 phones and 14 do not work by pressing key o or login button. Two of the phones do work. The other phones did work at one time and last night they stopped working. We use handsets that are plugged in to the side of the phone and when you want to login you simply press key o and you are logged in. I have taken the bad phones to the stations that work and it still does not work. I assume its the phone and not the tn or programming. Do I need to do an FDL on the phoness? Any assistance will be appreciated.