Stuck in gear

There is a spring inside this gearbox which is located on the shifter pawl that can break causing this. Does your gear lever move fully in both directions? I have seen stones getting lodged between the shifter arm and gear case stopping the lever moving in one direction.

bettr git the bike to a trans specialist for a testdrive--it may need rebuild or the clutch mech has issues

Rock the bike gently forward and back while shifting into fifth gear. Now push the bike forward while sitting on it and see if the rear tire turning will turn the motor. If not, your motor is stuck. If it turns, you have a kickstarter issue.
Many people never learned to depress the kickstarter down until you feel it engage before kicking it through. Kicking from the top slams the gear teeth together and causes damage. You may need to pull of the engine cover to determine if there’s damage.

You might have bent the shift linkage that is beside the transmission.

Clutch discs are stuck, put the bike in gear, not running, pull in the clutch and push the bike back and forth to break the clutches loose. Once they break loose start the engine put the bike in gear, hold the front brake, and slip the clutch a little to remove any built up or stuck crud on the plates.

With bike not running, rock the bike backwards and forwards and shift through all the gears. If it shifts all the way to fifth gear and back down, then the problem is not in the transmission. If you can't shift the transmission into any gear with the bike not running, just rocking it backwards and forwards, then you've got a problem with the transmission or the shift lever mechanism.

If it does shift but you still can't get it into gear something is strange. I've seen a clutch that the plates were locked together from sitting up, but it still would shift into gear. Of course, when it did shift into first gear, the bike would lurch forward and kill the engine. In this case, we had to disassemble the clutch pack and free the plates up. If you've had a new clutch put in the bike, it could simply need an adjustment. But, usually a new clutch will have a tendency to wear in and start to slip rather than drag. When a clutch causes the bike to lurch when put into gear or become difficult to find neutral with the engine running, it's dragging. I'd check the entire clutch adjustment to start with.

Slide the rubber boot on the clutch cable up, break the lock nut loose and turn the adjuster to make the cable as short as possible. Take the derby cover off the primary to gain access to the clutch release adjuster bolt. Break the large locknut loose, adjust the center bolt inward until you feel resistance. Back the screw back out and back in until you feel resistance again several times. You want to just take the slack out of the adjustment, not start to open the clutch up. Once you've turned the bolt in and feel the resistance, back the bolt back out 1/2 to 1 complete turn. Hold the bolt in this position and lock the lock nut again. Now, adjust the clutch cable back out until you get a freeplay of about an 1/8 inch at the lever. The clutch should be adjusted well enough to release at this point. If it doesn't, the clutch plates are probably stuck.

If the clutch plates are stuck, rock the bike back and forth and shift the bike into fourth or fifth gear. Now, while holding the clutch lever in, push the bike backwards and forwards far enough to "bump" the clutch. This may break the bond between the plates and free it up. If not, you'll have to disassemble the clutch in order to free it up. Good Luck.

i had the same problem mr tombones is correct it was the bar that runs through the selector forks was bent

Sounds like the syncranizer is bad