If your car won't go into reverse, it could be due to a few reasons such as a low level of transmission fluid, a faulty shifter linkage, or a bad transmission. A low level of transmission fluid can prevent the gears from engaging, so it's important to check your fluid levels and add more if necessary. If the shifter linkage is faulty, it may prevent the gear from engaging when you try to shift into reverse. Another potential issue could be a bad transmission, which may need to be replaced or rebuilt. You should take your car to a mechanic to properly diagnose and fix the problem.