No 12volt power

First a little background information. I have a 2004 Jayco Class C with E450 chassis. Have not been able to use it in several months, but I do like to run the generator every so often to keep it working. For quite a while, the coach battery has been very low, so in order to start the generator, I just crank the V10 up, let it run a couple minutes, switch on the battery disconnect switch, and the generator gets its cranking power from the engine. However, today I went to start the generator and nothing happens. When I tried to switch on the disconnect switch, none of the 12volt lights or anything works. So my question is, do you think it is another bad disconnect switch or what. I replaced one about 9 months ago but it had different symptoms at the time. Also, if the coach battery is COMPLETELY dead will that cause this problem. Anyway, any advice or suggestions are appreciated.