Having many what seems like electrical problems, but most concerned that there is no signal to the OBDII port.

I have a 1999 Plymouth Voyager. After asking someone to take a look at why the exhaust fan and why it wasn't kicking on causing my van to overheat, not only was that problem not fixed, more problems were created. Now, I have to make my 6 poor children ride around in a cold van with no inspection, and soon no registration. Here is a list of the problems: The van overheats sometimes if left running, the inside lights and the locks will not work unless the van is on, and strangely after the van has been running if I do not turn off the headlights before turning off the van, then the locks and inside lights will still work until I turn off the headlights. The stereo doesn't work at all (all I hear is a pop in the speaker when first turned on), and now there is no signal to the OBDII so that I can get it inspected. All the fuses seem ok. I would EXTREMELY appreciate any help whatsoever!!! Please??
Concerned Mother