Welcome to the forum. This question may be better posted in a different section of the forum, but I will address some possible items to check.
1) Gauge - if you pull the wires and cross them does the gauge move? If so, the gauge is okay.
2) Float - the float could be stuck or filled with gas. See if it moves in the chamber or is full of fluid.
3) Fuse - there are odd "fuses" in the float chamber that can be blown. There are specific threads in this forum that can address how to fix this issue without having to purchase a new unit.
Good luck!!!