Google: Android Phone Hang / Freeze

If the phone is not working correctly ( hanging or freezing ), you may need to master reset it and also clear the cache partition. These two resets clear different parts of the phone storage. Unlike a master reset, wiping the cache partition does not delete your personal data.

<< Wipe cache partition >>
To wipe the cache partition, follow these steps:
1.  Turn off the device.
2.  Press and hold the following three buttons at the same time:

Volume Up key
Home key
Power key

3.  When the phone vibrates, let go of the Power key but continue to press and hold the Volume Up key and the Home key.
4.  When the Android System Recovery screen appears, release the Volume Up and Home keys.
5.  Press the Volume Down key to highlight 'wipe cache partition'.
6.  Press the Power key to select and wipe the cache.
7.  With 'reboot system now' highlighted, press the Power key to restart the device.


<< Master reset with hardware keys >>
A master reset restores the original factory settings and may delete your personal data on the internal storage, such as downloaded content, ringtones, images, apps, and contacts. It does not delete data stored on the SIM card or SD card.

If the device menus are frozen or unresponsive, you can master reset using hardware keys. To perform a master reset, follow these steps:
1.  Back up all data on the internal memory.
2.  Turn off the device.
3.  Press and hold the following three buttons at the same time:

Volume Up key
Home key
Power key

4.  When the phone vibrates, release the Power key but continue to press and hold the Volume Up key and the Home key.
5.  When the Android System Recovery screen appears, release the Volume Up and Home keys.
6.  Press the Volume down key to highlight 'wipe data / factory reset.'
7.  Press Power button to select.
8.  Press the Volume down key to highlight 'delete all user data.'
9.  Press Power button to select and start the master reset. When the master reset is complete, 'Reboot system now' is highlighted.
10.  Press the Power key to turn the restart the device.


Reference:
Help with my Galaxy S3 - Freezes 12 times a day.
http://www.sammobile.com/forum/showthread.php?t=13216