Q: Prius won't turn on, go into drive or reverse.

Load test the smaller 12 volt battery, that is located in the rear right trunk area. Of course, be sure that 12 volt battery is properly connected, too, as it might have been disabled during the high voltage battery replacement. If the 12 volt battery is OK, the vehicle will have to be diagnosed, step by step, per what is a pretty long diagnostic decision tree published in the Factory Service Manual. There are a lot of tests, they have to be done in a specific order, and if you don’t have the manual it is not possible to do. If you desire, YourMechanic can dispatch a certified mechanic to your locale and get this resolved, including performing the battery load testing if you want the mechanic to do all of the diagnostic work. If you want to go that route, please request an electrical circuit/component diagnostic and the responding certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.