Hey there, rb413!
It's hard to say what may have happened to cause this.
If something like this ever happened again, you should proceed with the steps of soft resetting the device.
If that works, you can then proceed with the factory reset http://bit.ly/Udl5Ac.
If you still aren't able to factory reset the only other option would be to replace the device if it is still under warranty with no physical/liquid damage.
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This is a somewhat common occurrence with my Strat. Seems to be common to this device in general looking at the number of times this is asked on the Internet....
The way I fix it is to go into recovery mode. The first link that the support tech supplied above is absolutely no use (does that tech even know what a boot loop is??) as you cannot get to the powerdown screen, because the phone never boots up (just flashes the Samsung logo over and over as it tries and restarts...).
The second link is just a copy of the first link and is also useless in this case.
What you want to try is the "Alternative Method" listed about halfway down this VZW help page: http://support.verizonwireless.com/clc/devices/knowledge_base.html?id=47757
The alternate method will reboot and fix this problem. You will have to go through initial set up, add Google account, and re download any extra apps. You will be prompted to sync contact from VZ backup. It will not effect contents of SD card.
My phone had been running slower and slower for a month or two. It would take a minute or more for dialer to load. Finally it went into boot loop. Now it is fast again. I believe the reason for the problem is that when you get close to filling up the 2.19GB of internal memory [out of 4GB] reserved for apps this slowness and behavior starts. Keep track of this from settings menu or task manager.