The problem is
ProxSensor==LOW is false so 0. you read the pin 0 and the outcome is random. The surrounding wiring can affect that. If digitalRead(0) is zero the wav starts playing immediately again. At least use
while (digitalRead(ProxSensor) == LOW);
The TMRpcm and one of your other libraries might use the same timer on Uno which causes one of them to break. Either get a Arduino Mega which can run TMRpcm on TIMER3,4 or 5 or use libraries that don't require a timer.