I don't know what vehicle you have, But our 2000 Ford exp. lost a screw out of the steering colum and wouldn't go into park. Once the screw was replaced no problem shifts fine.
Broken cable or linkage? Transmission trouble (?)
The gears in your transmission may be sticking or worn out. This would cause your transmission to not be able to shift.
Shift cable adjustment, low fluid, internal transmission failure.
It is on the side of the transmission where the shifter cable bolts to. It is built into the neutral safety switch.
If it still has a reverse, just in the wrong place, then the linkage or cable from the shift lever to the transmission has streched or fallen out of alignment.
Because it is usually a mechanical cable that is connected to a front axle or the transmission. Newer cars relay this information electronically and will show the actual speed when in reverse.
its a cable transmission
Might be the sifter cable binding. Could be transmission itself, but just check the cable by disconnecting it from the transmission and moving the shifter... If it moves then its trans, if not then just replace the cable.... My trans went out in my spirit and im trying to fight to get a trans for it, I have a guy who has one but he wants 150 and I cant afford it... But im trying.
Start by removing the gauge cluster, unhook the speedometer cable from back of cluster. Pull speedo cable thru the firewall, follow it down to the transmission, and then unhook it. Install in reverse order of removal.
The cable that runs from the throttle body to the transmission is the detent cable. The other cable is the speedometer cable.
Is it an automatic? Time for a new transmission... If a stick and 1st, 3rd, 5th are ok, then you have a possible shift cable problem. You should be able to see them on top of the trans. If everthing is moving properly the trans has an internal problem.
Check the level and condition of the transmission fluid. It should be red light cough syrup. Perhaps the transmission cable is damaged. If the fluid looks fine, and the cable seems tensioned, you're probably talking about transmission failure.