[whynotthinkwhynot]

Check your negative battery terminal. You can check the main negative (big wire) that goes to the engine, but I'll bet that the 2 small wires that are connected to that terminal via a stud and nut are damaged. Look for cracks in the ring terminals on those wires. I would remove the nut and pull those wires off to inspect. When mine broke, they looked connected.

After checking or repairing those wires, look on the front of the engine on the valve cover. It's best to just walk over to the right side of the car. There is a black rectangular box that has a small black wire going to it, and another small black wire coming out that goes to the strut tower. Pull on those wires and make sure both are good. If the wire going to that box from the engine harness breaks and shorts out, it will cause you to blow the ECU fuse. Check in your owner's manual, and check that fuse. Replace it only with the exact same size fuse if the fuse is blown.

You should also check your alternator output as mentioned by others when you can start and run the engine. Also, a bit of grease under the battery terminals prevents corrosion. I coat mine in grease. Any old grease will do.