clutch

I have a 75 mgb
when the car in not running it will go into any gear
when i start it it will not go into gear or change gears
does anyone know what this could be

Have you check the resevoir for the clutch master cylinder?

If you have fluid in the clutch master cylinder and see no obvious signs of leaking do this. Have someone push the clutch pedal down while you check the movement of the push-rod connecting the slave cylinder to the clutch fork. It's on the passenger side of the car for USA left hand drive cars. The push-rod should have about 1/2" of travel if it is working properly. If not you have a hydraulics problem. It could need bleeding or either or both cylinders may need rebuilding.

Clifton