Before doing anything, I would back up any data, to a computer or other device, as to keep from losing any personal informaion.
Now I suggest you try a soft reboot (if you haven't already). Turn off the phone, remove the back and battery, wait 1 to 2 minutes (at least). After the time has passed, put the battery back in, the back on and restart the phone. This is the most common fix.
If this doesn't fix the problem, then I would next check and see what software/apps were installed and/or updated right before the problem started. Especially since your phone is from a different part of the world, it is completely possible that an installed app or app update could be conflicting with the phones software. If you did install or update anything just prior to the problem, I would suggest removing the installed application or removing the update.