My car starts, but will not shift into any gear. Once I turn it off though, it will shift into gear.
You have not stated whether this is a automatic or manual transmission. This information would make a big difference. If the car is a manual then the most likely cause is a clutch issue. If the car is a automatic then the most common issue is an electronic issue. A qualified mechanic, like one from YourMechanic, will be able to diagnose your transmission and perform any repairs required to get you back on the road.
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