Power Issues creating sensor read issues

The Maxsonars run at 3.3 or 5V, but they probably have a large current draw when pulsing the
transducers. You may have cooked the tiny 3.3V smt v.reg on the pcb. If that's the case, you
could unsolder it, and solder in anything for a replacement, like a TO-92 part, or even an
LM1117-3.3 on a couple of wires.

The 328 itself will no doubt run at 5V, but doubtful the wifi module will run at that voltage.
You may have accidentally applied 5V or 7.4V to the 3.3V buss sometime in the past, and
cooked either the v.reg or the wifi chip, or both.

If you figure the board is basically toast, you might try replacing the v.reg as in the first
paragraph.