What will cause a gas gauge not to work

My roommate has a 2003 Dodge Strautus, two months ago his car was rear-ended. However,

there was not to much damages but his gas gauge stop working. The gauge stays about 3/4 full. Question what should he do?

The float level in the gas tank is probably stuck. The tank will need to be dropped to access the mechanism, and determine if it can be loosened back up and adjusted or needs to be replaced.