I buy my i pHone 3s snice two year back. Now i am in Saudia Arabia. I upgrade my I Phone, BUt its stop working.
So i can i fix this problem
You can't. The phone is locked to US AT&T and won't be unlocked by either AT&T or Apple. If it was previously working in Saudia Arabia, that meant it was previously hacked by someone to be unlocked and upgrading the software locked it back to AT&T.