Autohelm Bidata

Our 3rd weekend with our 1996 Oceanis 285. Our speedometer stopped working. Several hours later the depth finder stopped too. Both display 0.0. We've tried turning the unit on and off numerous times, pressing all the buttons, including reset, to no avail. We did ease into some river mud going very slowly early that morning, and backed out very easily -- the depth finder was working at that time, but don't recall if the speedo was -- as we were getting ready to dock to re-fuel.
We were healing pretty well after w re-fueled and started sailing before the depth finder stopped. For a while the depth finder did display some wacky numbers -- 385 and 435 -- and showed a little arrow pointing up and one pointing down. After than, back to 0.0 for the rest of the day.
The transducers look fine, as does the wiring that I can see.
Any thoughts on where to seek out the problem? Did I stir up a bunch of river mud when I hit reverse to back out of the mud?
Many thanks! Ooooo Baby!