Nuvi 2555mt lost voice - Garmin nuvi 260W GPS Receiver

First, do you hear beeps when you press a selection on the screen? If yes, then your speaker is OK and the audio circuits are OK in the unit. Make sure that you have a voice selected in the voice menu. Some units have an audio mixer screen and provide different volume settings for navigation (voice) and system (beeps). maybe the volume for the voice (navigation) is set to off. If you don't hear any beeps when you touch the screen AND you don't hear a voice, make sure that the sound isn't set to be muted. If the sound isn't muted, you may have a defective speaker. More information on audio issues can be found here:
SHARCNET USA Out of Warranty GPS Digital Camera Repair