Now the radio, cruise, electric door locks, do not work

The radio, cruise, electric doors & truck have all stopped working - what could be causing this? (New Battery etc, this is additional issue). 1999 Mitsubishi, Eclipse:

Replaced the Battery: Other new items also. Garage is doesn't have an answer!
Originally the car would "die" at intersections and when coming to a stop.

They did some stuff, but now the radio, cruise, electric door locks, do not work. The trunk leaver is pulled, but will not release the trunk!

My son's car! He's working but for $8.00 per hour/ I can't spend anymore on this car, and he's wanting to start school in January! _ HELP!