After traveling about 8km my car wont go into 1st or reverse gear. when it is cold it goes into all the gears fine. when i switch the car off it will go into gear. we did put a new(aftermarket clutch) in a week ago. it is a 2000 mazda 323 1300. can you please advise.

Cluth cable ajustment if equiped.Some cars have a cluth cylender if your model has the cylender no ajustment is available.If you had your cluth changed at a garage you might consider takeing it back in for ajustments.If you changed the clutch check cluth cable for ajustment if your car is equiped with cable if not i would perhaps remove the transmission and inspect clutch for loose clutch plate or release bearing might not be seated properly hope this helped you.