If you are experiencing issues with your Sprint Blackberry 9670, a factory reset is the way to go.
Perform a factory reset
A master reset will return the handset to the default factory settings and erase all personal information on the handset.
This type of reset should be used as a last resort to fix major errors, and all important information should be backed up before proceeding.
From the home screen, scroll down to open the All tray.
Scroll to Options and press the trackpad.
Scroll to Security and press the trackpad.
Scroll to Security Wipe and press the trackpad.
Scroll to and check the desired options.
Enter blackberry in the field.
Scroll to Wipe Data and press the trackpad.
The handset will completely reset and restart