Probe=Problems

Okay.I need help. My boyfriend knows nothing about cars. I even have to change his filters, oil. Basic maintenance for him. So when his Ford Probe started acting up he called me. The problem description:

All electricals work before cranking the car: lights, radio, etc, but when you try to turn it over you hear a click and nothing happens. It won't turn over and all the power is drained.

I tried: Testing the battery, changing the battery, charging it, checked ground and + cables, had the solinoid and starter benck tested/tested. There is nothing wrong with any of these. The starter starts like new, the cables ARE new, and the battery is perfect. What am I missing?