I was in a fender bender a few months back that broke the radiator. Before I knew the radiator was broken I drove it home, and while it was not in gear it would rev up and down on its own. On the way home the temp was really high but it never stalled or broke down.a few months later after replacing the radiator it would start but would still rev up. The next time I tried to start it... nothin happened the car wouldn't turn over just a buzz sound would happen when I turn the key. The battery is fully charged and everything on the inside comes on.whats wrong

Read sections A and B in the link below:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-honda-civics-46563.html

The buzz could be the main relay or a problem originating in the ECM that's manifesting itself in the main relay (run the K-Test). It's best to run through the tests in the above link and see where it leads you.

Number one rules for Hondas."DO NOT OVERHEAT THEM". Dude you could have any number of things wrong. Do the common sense things first. Make sure the engine isn't locking up. Make sure the starter is good. Jump the ignition feed to hot of battery. If it cranks, your problem is in the electrical part of ignition system. If it doesn't and buzzes, then you need to look at starter itself. You probably know in your heart what is wrong because problems like this don't just show up on Honda's. It is probably as you already know, related to the radiator busting and overheating engine. If the radiator busts, you shouldn't wait months to replace it unless you are absolutely NOT driving the car.