transmission, or Linkage to front gear shifter

My transmission was running just fine, until, I parked my car. Then shut it off and went inside store. I came back out got in car started the car all like I usually do. Then went to put automatic gear shift into reverse to back out off parking space. My car made a kinda loud thud. Or small sounding bang. Then I put the car back in park. Let car countinued to runfor a few seconds and tried again. Then I checked if it would go into any gear. It would no longer shift into any gear. What could this mean? Besides replacing a whole new transmisson? Thank you,

Maggeez