Welcome to Android Central! Are you rooted or unrooted? Go to Settings>Language & Input--under Keyboard & Input Methods, which keyboards do you see? If you see your usual keyboard or Google Keyboard, make sure it's checked and listed as Default. If you don't see any keyboard, go to Settings>Apps>All, and see if the keyboard got disabled somehow. Depending on your Android version and manufacturer UI, disabled apps may show up in the All list (possibly at the very bottom), or in a separate Disabled list.