Try quitting the messages app then reset the phone.
Double click the Home button to show the screen with running and recently used apps. Each app icon will have a sample page above it. Flick up on the page (not the app icon) and the page will fly away and the app icon will disappear. This quits that app. Then reset your device. Press and hold the Home and Sleep buttons simultaneously until the Apple logo appears. Let go of the buttons and let the device restart. See if that fixes your problem.