While driving on freeway going 75 MPH using cruise control, my engine stops running. I still have lights and power but no power steering or power brakes because engine was off. I put it in neutral and coasted off freeway and into gas station. Tried to start it but it would only click once. Took out the alternator had it tested and it failed, so I replaced the alternator. Tried to start it and only hear a click, even with jumper cables it would not turn over. Any ideas what might be wrong? I had my battery tested it is good.
@hellomoto is right with his comments: with the alternator gone out, the battery was run down to the point where it's not going to start the vehicle, let alone run it.
Whether or not the battery is a complete waste is yet to be seen. What you need to do is get the battery onto a charger (2A charge rate) and see if it will take a charge. Running a battery down to where it won't run the vehicle is not good for it, and will have shortened its lifespan. Putting a charger on there is going to either give it the charge or it won't. Before you lay out the cash for a new one, this is the right first step.