My Chrysler 300 trunk won't open. I tried fob and inside button.

Hello, sounds like the motor for the trunk release is not functioning any more. If there is no external key cylinder on the trunk, you'll have to find a way to get inside the trunk to access the release, possibly via folded down rear seats (if equipped). Then, diagnostic testing and repair can occur. Before that, I would recommend a diagnostic tool be used to check the operation of the trunk actuator, this should be something that can be checked. This would be in case there is some sort of control issue, which may have been in play when it opened by itself.