1998 Plymouth Voyager CAN YOU HELP ME DETERMINE WHATS WRONG

I HEARD A BIG BANG THAT SOUNDED THAT LIKE IT WAS COMING OUT OF THE BOTTOM OF THE VAN THEN AFTER THAT THE ENGINE WAS ON BUT THE VAN WOULDENT RUN ON REVERSE OR ON DRIVE IT JUST WOULD SOUND LIKE IT WAS IDELING BUT NOT MOVING