Why can't I see my messages on my iPhone?

I've had this iPhone 4S for about 6 months and just today I went to check a text and they are gone. I mean it won't even let me send a text or anything. The whole screen is blank when I go to it. Any body know why this might have happened?

The software must have shut down. Try a reset.

Go into settings then scroll down to iMessage and then turn it ON and it will help, if it is already on then you may have to many apps open and or not enough memory

I turn off my phone & my msg deleted or disappear