HELP... Maxima RPM guage needle got stuck

The needle on my maxima's rmp guage got stuck every once in awhile (auto trans). Since it's auto trans and only happen once in awhile, I didn't pay much attention. However, lately, the rpm needle stop working. It now only goes up and up as long as the car is running, it only come down when the enginee is shut off. Can anyone tell me what went wrong?