my samsung galaxy s3 keeps restarting

[arafa ferdous]

i upgraded my samsung galaxy s3 (GTI9300) using WIFI since then my phone keeps restarting. i went to samsung showroom and they flash my mobile and then installed the version 4.2.1 which i suppose is unofficial. now my phone keeps restarting while using it and sometimes get hanged. It would be very helpful if you provide me with solutions. Thanks

 

[ErinGoBragh]

If Samsung messed up your phone, you should take it back to them to get it fixed. It sound like the version of android they installed has serious stability issues, in which case you want a different version installed and they should know that it isn't working correctly.