No start No crank

So I bought this hearse as my first ever project car. I am positive the base of this hearse is a 1970 Cadillac Brougham. I got this one since it was still running and road worthy. The guy I bought it from had it as his daily driver and did regular maintenance on it. Drove it around for a couple days after buying it with no issue. As I was parking it at the end of the day I turned it off to unlock the back before I pulled in to my space went to turn it back on and got nothing. The car clicked once and then nothing after that. Looks like there is no power getting into the car since none of the lights inside are working either now. I tried giving it a jump but the battery seemed to still have juice. Would this be a fuse issue, wiring, starter, alternator? Any help would be appreciated I am very new to this.