My iPhone messages won't open?

Every time I click the little app to open my messages it'll open, but, I can't see any conversations and it'll stay on that screen for about 15 seconds and then flashback to the home screen, any idea what's wrong? :( it's an iPhone 4

I have had this before and i have an iphone 4 too!;-)
What I did was I turned my phone of let it rest for abit then turned it on again and it worked! You need to let your phone rest for abit as it might have crashed hope it helps