So I just acquired a Samsung galaxy S3 running Android 4.3 with Clockwork mod recovery off friend, and last night it ran out of battery. Then I tried charging it. It's not charging or turning on. Any ideas what's going off?

The battery has probably run too low, because the phone turned off too late.
Connect your phone to a charger (not a USB port) and let it there for a few hours (I would say at least six). Keep an eye on the battery's temperature and physical appearance.

@Scade I originally thought that but it's been on charge all night... The charger is working with 2 other devices too...

Charge it and hold all buttons for like 10 minutes until the screen turns on. Thats what helped me when I had this problem.

@Jifuna I've already tried recovery mode if that's what you mean...

@DucksCanCode No, I mean all buttons so volume up, volume down, home button, power button. And hold it while charging for like 10 minutes if you're lucky you're phone will turn on after a few minutes.

@Jifuna I've never heard of that working, but it isn't doing anything now

@DucksCanCode It worked for me and I red it on a forum. Just trying to help though.

@Jifuna I get it, thanks anyway mate