The phone hang when I want to write msg

..first revise the software you have installed and try to uninstall the latest software - you may be recognized that this problem appeared since you have instelled some software isnt it? If not then you have to hard reset your device (as ussually in such cases) - also described somewhere here.. (dont forget you will loose all your data):

1. Turn off the LG KS-20 completely (do this by pressing and holding the power button and wait for the prompt).
2. Press and hold these three buttons–volume down, Call and power–till the LED (this is beside the front camera) flashes.
3. Release the buttons. That same LED should flash blue/red/green and power up.
4. The KS20 should be in a clean state.

try to install any anti virus for mobile