Sounds like Email needs to be reset: Open The Mail app. While it's grey/unresponsive, hold down the Sleep/Power button until you see the "Slide to power off" screen. Instead of sliding, press and hold the Home button until the Mail app screen goes away and you get put back at the Home screen.
If you open the Mail app now, it should be back to normal.
That is called killing the app and is useful when any app is frozen or acting weird. It doesn't delete anything, so don't worry there.