What year and make?
1999 ford explorer 4.0 manual transmission gear shifter wont fit on shaft
you most likely need a new clutch
most likely the clutch & pressure plate is shot.
it wont change gear properly. if at all,,, because of the oil thickness
If second is the only gear that does not work, there is an internal failure. The transmission will need repaired or replaced.
It is quite possible that your clutch is not disengaging the transmission from the motor. Also, your synchros could be bad, which would not allow it to go into gear.
Sounds like a bad clutch or pressure plate
Check if the clutch is working properly.
Gear up then
there are a few reasons why this can happen but the most likely is a problem with the slave cylinder
you either got air in the hydrolic clutch or the hydrolic clyinder is out .check your fluid level.
Trade it on a more reliable built auto! My Mercedes has 300 + thousand miles with no trouble. Hope this helps.