iPad 3 - when I click on the email icon, it quickly pulls up the email but then it disappears! I click on the email icon as usual, but it just quickly pulls up the email and then disappears.

What's going on?
Welcome. Is your device jailbroken? If so, have a go at updating cydia. If not I might need some more information. What did you do before the problem appeared? Have you had the problem for a long time?