This will get you the stock wire colors that went to the original factory radio, you'll still need to test em to see if they are running. If you have several wires coming out that are all powered and don't go to anything, I would cut them short and tape them off so they don't ground out and blow fuses. If the previous owner ran new speaker wires then you'll have to find the wires and determine what is positive and negative and wire that to the new radio harness. If you can't find power wires you can run new ones from the ignition harness that comes out of the main fuse block and goes to the key cylinder. I would only wire that up as a last resort.
As for the engine not turning over it sounds like you blew the ignition fuse, which is one of the main fuses under the hood. you'll have to pull the fuses and visually check them to see if they are blow. You'll also need to be aware of why it blew in the first place. The main power wire probably touched a part of the frame or the ground wire and caused it to take out the main fuse. It is really important that you work carefully after you determine what wire it is make the connection and tape it up.
I hope this helps you out. I know where you're coming from, I did car stereo install for 5 years and had customers like you all the time come in with a rats nest of wires and whole lot of problems. Good Luck