Is your phone plugged in

 

I have found that after rooting my phone that if I shut it down while its plugged in will continue to reboot ..I have to unplug my phone to start it..

 

I've read it's difficult to root the Prism.

You should be able to do a factory reset of the phone by holding down the power and volume-up buttons. A menu will eventually appear, use the volume-down button to scroll down to factory reset. This procedure will un-root the phone.