2004 Chevy Impala speedometer problem

I'm assuming you have the analogue speedometer. (Needle that sweeps left to right) If you're aren't getting a "check engine" light, then you can eliminate you vehicle speed sensor as the problem.

You speedo operates off of electricity. There's a small electrical motor on the back of your gauge cluster that receives a signal from you computer telling it how far to move.

If the rest of your gauge cluster functions, then it's not in the fuse, computer, or wiring leading to the gauge cluster. This leaves the speedo motor, or the part of the circuit board that controls the speedo.

I've repaired gauge clusters before, but it requires a circuit board diagram and a volt/ohm meter to probe the resistors, motor windings and circuit traces. If you aren't familiar with this procedure, your only recourse would be to replace it as a unit.