Car will not start or even turn over

A while ago I went to start this car. I noticed that the headlights were becoming dimmer so I shut it down to re-start it. It would not turn over at all. I checked all the obvious; i.E. Battery/alternator and various electrical connections. The inside of the car powers many but not all of the dash lit components and I hear what sounds like a component running on the right side of the dash. I tried the diagnostic screen but there is no power to it. Also the fuel data control center shows an empty tank all the time except for immediately after filling up and all the other feature are obvious wrong (the data center has been tested and is fine). Do these problems sound like a body control or engine control module? I have not bench tested the starter yet because these additional issues lead me to believe that it is a module? What is the likely suspect and which should I check 1st?

Thank you for any and all help - this is getting frustrating and I do not wish to pull the starter if nothing is wrong with it.

Thanks again

Andrew