while working on my phone suddenly it stops and shows "SAMSUNG" it remains in this state for hours, to run again the power botton shall be hold for 7 seconds then it restarts.
Welcome to Android Central! How often does this happen? If you have an SD card inserted, try unmounting the card and removing it, since a corrupt file on the card can cause issues. If it persists, try also booting into Safe Mode, since one of the apps you installed could be causing the instability: https://support.t-mobile.com/docs/DOC-37190
