95 Sedan Deville-Computer Issues, Help.
 

I have a 95' Sedanssssss Seville and we needed to replace the battery so we did, and now the car has stopped running and anytime you try and start it, the horn honks like crazy and the trunk pops. So im assuming that there's a issue with the security system and the computer needs to be reset. I've already attempted to take battery cables off, and touch them together and leave them off but no such luck. Any help would be appreciated, I don't want to bring it in, I don't have the money. Thank you!