No power no lights no nothing

If the battery is good, but there is no power to anything, (ANYTHING, not even a little light in the cabin), and the leads are properly seated and not corroded at all (any corrosion or rust could interfere with the leads ability to draw power, disconnect the entire battery and use sandpaper to clear them. Google first to ensure sandpaper won't damage anything), it could be a few things. You should take it to a mechanic for a diagnosis. It could be a fuse, but whenever I've had weird electrical issues on my used vehicles that had been the result of a blown or damaged fuse, I'd at least had one part of the car still get power, if not most areas. It could be a short, I have no personal experience with those, but I've heard a short affecting the main wires can have the symptoms you describe. Be careful, and unhook the battery when following the wires. Shorts can be due to a wire being frayed, or the protective coating on a wire being worn off and the core (what conveys the electricity) touching metal, such as the frame. This can mean that touching the metal that touches the wire's core has the ability to shock you. Finally, in my limited (note, I am not a mechanic nor do I fix cars regularly, my experience is limited to my 4 used cars I've owned) knowledge, if you attempt to turn the engine over (start the car) and don't even hear it try, just clicking or not even that, it could be the alternator. But from my understanding you'd still be able to draw power from the battery for some systems, even if the car didn't start. I'd suggest a mechanic unless you have the knowledge and ability to diagnose these issues yourself. Certain car models may do things differently than others. Some could have safety mechanisms that cut off all power if it detects a short or damage, which could mean your ability to diagnose the issue yourself is hindered unless you know about it.

If you didn't get it running try looking under the carpet in the back passenger seat and you will see a metal box under there with a red thing holding them together pull those wires out and see if it starts my 04 grand prix dis the same thing