I was backing up in my driveway and I felt a bang and then all of a sudden I have no reverse...I can still drive forward...can someone help me...am I screwed ? do I need a new tranny?

 

Which transmission do you have? A standard is far easier to repair than an automatic, which usually is just swapped for a reman.

Also, this question should be over in the transmission section as it has nothing to do with the engine.

 

You likely have a broken reverse band in the transmission, which is a common problem. Time to pull the transmission apart.