Why is my android OS upgrading and booting every time I turn my phone on?

[AC Question]

Hey, I am Nick and I am using a Samsung Galaxy Light SGH T399 with Android 4.2.2 Operating system, I don't recall if I deleted or uninstalled one of the built-in programs or apps, now my phone starts crashing every time I am using it, It says system processing isn't responding or I should close it. I have lost all my contacts, files and other downloaded apps. I don't know what to do now. Is there any possibility to reinstall an other updated operating system and get all my files back?

Thanks