by dip switch I assume you mean the control type selection switch on the rear of the unit. In position 3 it sets the unit to respond to IR. In position 1 it sets the unit to respond to RS232.

Your problem could be anyone of a number of things. I would suspect blown RS232 receiver/driver chips due to some electrical issue. I'm assuming that the code has not changed and there are no disconnected cables, and whatever you are using to convert the Pronto output to RS232 ihas been checked and is functioning.