Welcome to the forums, Androidnewbie (you'll have to change your user name after a while
).
Anyway, the JB reboot issue is being reported across many Android devices, and the remedy seems to be a factory data reset right away. I recommend also shutting the device down first, then removing the battery, sd card and SIM card then waiting a minute or so prior to the reset.
Don't bother to power up once you've put the battery and cards back in; just hold down the home + power + volume up keys until the white "...galaxy..." letters appear on the screen, then quickly release all three buttons.
Once the blue recovery menu appears, navigate to the factory reset item using the volume down key, then press power and let it happen.
Once done it'll highlight on the "reboot now" item, press power again. That's it.