Colson4000

I have a 5spd 1.8 4000, and have discovered something strange. The car idles and stays in neutral just how it should, and goes into 1st gear how it should. However, it does not engage any other gear, and instead stays in 1st when changed. This is the case with every gear, even reverse.
How would I fix this? Would replacing a brand new clutch kit solve it, or would it be something else?
A little context: the car was parked for around two decades by the previous owner and not moved. My guess is that it has been engaged in gear for so long it does not bite any others, but I have no further clue.
Any comment helps, thanks.

Rogviler

I would start with the linkage and make sure it's moving correctly. There's a pivot point pretty much right on top of the transmission that has a plastic insert that wears out. It's a common failure point. So check that and I know there are several good replacements out there, it's just a pain to get to. You'll probably have to jack the car up (securely) and have someone try to change gears while you observe from underneath. It would probably also be worth checking the fluid in the transmission to make sure that there is fluid and that it's not all water or something. I forget the spec for the fluid, but it's basically gear oil.

Rossfeld

Be careful on the jack points too, some of the underside is a little flimsy when the car settles.