A clutch does not go into gear. A clutch engages, Normally if a clutch fails to engage it is because it is worn. with a worn out clutch you are able to start the car in gear without your foot on the clutch and the car wont move. Normally before this happens you will notice what is known as a slipping clutch. A slipping clutch means that the engine is turning faster than it should to keep the car moving while in gear. once this starts to happen it does not take long for the whole show to come to a stand still.
If you have bleed the system and If it will not go into gear with the engine running, the clutch pressure plate may have failed.
1999 ford explorer 4.0 manual transmission gear shifter wont fit on shaft
synchro plates went out
The clutch is bad or out of adjustment.
Because your transmission is broken. When a car wont go into gear(s) there is something wrong with the linkage, the transmission control system ( electronics on some newer vehicles ), the clutch or the the transmission itself.
How long after you had it fixed
The throwout bearing in your clutch is the likely culprit here. Your clutch may be shot in addition, but you are probably looking at a costly fix here.
you most likely need a new clutch
If it will shift when the engine is off, but not while it is running your clutch is not working
My first suspect would be the clutch. Have a competent mechanic take a look at it.
If it will go into gear when the engine is off but not when the engine is running, the clutch is not disengaging. It could be the clutch, possibly warped or put in wrong, or it could be the hydraulic clutch mechanism.
Could be a broken clutch fork, linkage, or cable depending on the setup.