Sounds like your having a shift/lock issue. This could be the shift lock solenoid at the shifter, a brake switch, voltage issue or a shifter issue. Hard to say without accessing the items and pulling voltage reading at time of actuation.
Now, what concerns me is the "pounding, hammering" to get in and out of gear. I am hoping, in the process of getting it in and out of gear, something else was not damaged.
First step, diagnostics. If your not handy with a volt meter or test lamp, and do not have the patience with disassembling a shift mechanism, do not attempt. Get a QUALIFIED technician.
Hope I was of some help.