You will need access to programming mode for both problems, In order for the phone to pick up on a particuler line, That line has to be assigned to that set under "Terminals & Sets" sub heading "Line Access", whichever line you want that set to pickup on when coming offhook needs to be set as the "Prime Line" for that set under the same heading.

Your other problem is proably due to the phone system reverting to default, for some reason Nortel has the default setting for the lines as pulse dial. You will need to change from "pulse" to "tone for each line under the "Lines" heading.

If you are not familar with programming you may want to get a tech out. You may also consider getting the system repaired or putting on a battery backup. It sounds as though the battery that retains the system programming during power failure is old. Until that is repaired, you will likely have to program the system again each time you lose power. Good luck.