You're not telling us much. Is it still there? Are the wires still connected? Could the transducer have been damaged during a haulout or other work? Could the cable have been damaged? Does the depth sounder have it's own power supply like some Garmins and if so, is it getting power? Is it showing an error message?
Have you tried removing power from everything (not just turning it off) for a few minutes and then reconnecting the power?