If you are experiencing issues with your O2 XDA Serra, then a hard reset back to factory original may be the best option for you.
Make sure to backup your important data before proceeding.
1. Pull out the stylus.
2. With the device turned on, press and hold the VOLUME DOWN and ENTER buttons, then press the RESET button with the stylus tip.
3. Release the RESET button, but continue pressing the VOLUME DOWN and ENTER buttons until you see this message on the screen: