Alfa Romeo Repair: my transmission, evrey, 5th gear

Question
i have a manual transmission and evrey gear works besides 5th gear why is this my ahifter goes into 5th but it dont work and i dont see how onleyu one gear can go out  

Answer
which make and model and how many miles on it.  The fork  for that gear is bent or the bushing may have seized from low oil level. These are two of many possibilities on the generic
transmission.  Your specific application must be known to go
further.