Unhappy [Q] i9300(international) 4.1.3 upgrade settings issue even after hard reset

Hi All,
1. i9300(unlocked international) got an upgrade 4.1.3 after that my setting link wont work at all,
2. tried a lot of things but nothing worked and had to hard reset
3. After rebooting it opens the welcome page and "unfortunately, settings has stopped"
4. Called Samsung -> they do not support international unlocked phones in the USA
5. Tried odin but it doesn't detect on my computer (yellow/blue tab) although i can go to download screen
6. Tried to install 4.4.2(omni) /4.1.2 -apply update from ext storage but it fails "e signature verification failed"
7. My phone is not rooted, i cannot enable the USB debug option now as phone settings does not work.

How do i proceed ? Tried this link( http://forum.xda-developers.com/show....php?t=2163284) which says "flash ROM" /"flash gapps" but How? AM i missing something, i am not a developer could you please let me know in a layman's terms?