Hi Lyn. Check your unlock settings, because after the screen times out, it dims, then locks.
(Menu Key -> Settings -> Display settings -> Screen timeout)
From the Home screen, press the Menu Key, then touch Settings -> Location & security.
Touch Set screen lock/Change screen lock for these:
- None: Disable all custom screen lock settings, to use the default puzzle unlock screen.
- Pattern: A screen unlock pattern is a touch gesture you create and use to unlock your device. Follow the prompts to create or change your screen unlock pattern.
- PIN: Select a PIN to use for unlocking the screen.
- Password: Create a password for unlocking the screen.