Q: iPhone 5 crashed (blank screen recovery mode) the first time a week ago and did it twice today. What can I do to repair/prevent this?

my iPhone 5 has worked well until it started shutting itself off and rebooting some time ago. I did not think much of it as id heard of this issue with iOS 7.  a week ago (9/6/14) the phone just stopped working.  blank screen with no response from home or lock buttons.  Tried plugging it in to charge, still nothing.  When I connected to my computer, iTunes said the phone was in recovery mode and I had to restore it.  Today, 9/13/14, it did this twice.  What is happening and how do I fox/prevent it?