96 dodge caravan wont start

my girlfriend has a 96 or 97 Dodge caravan it wont start lights will go on radio,horn works same, but when i try to start it, it wont crank or anything its been doin it for some time now about 3 or 4 months we took it to a mechanic he said it was the sensor i think for the starter he changed it but its still doin the same problem......can somebody give me some advice.

my girlfriend has a 96 or 97 Dodge caravan it wont start lights will go on radio,horn works same, but when i try to start it, it wont crank or anything its been doin it for some time now about 3 or 4 months we took it to a mechanic he said it was the sensor i think for the starter he changed it but its still doin the same problem......can somebody give me some advice.
Do you get anything when you try to start it ? Might want to also try and clean all the battery terminals along with the terminals right on the starter itslef .