LG P504 User Manual page 18

Important notice
12. When the screen freezes
If the phone does not respond to user input or the
screen freezes:
Remove the battery, insert it again and power on
the phone. If it still does not work, please contact
the service center.
13. Do not connect your phone when you
power on/off your PC
Make sure to disconnect your phone from the PC
via USB cable when powering your PC on or off as it
might result in PC errors.
18 LG Optimus One | User Guide