You might need to perform a factory reset on the phone using the recovery - whether the phone is rooted or unrooted.
If it is unrooted, you do this by:
- charge the phone to 100%
- cold-start the phone with Send+End (so you are in FASTBOOT mode)
- use the menu presented to go to HBOOT MODE
- use the menu presented here to boot into RECOVERY
- when you see the screen with the Android on it (possibly a triangle w/ exclamation point), that is the "stock recovery" splash screen
- press Vol-Up+End
If that does not produce the (stock) recovery menu, press the Home soft-key + End
You should see a menu item that allows you to perform a factory reset.
If the phone is rooted, you have more options than this - but you didn't mention that.
eu1