HTC Desire A8181 - Your SIM card does not allo a connection to this network

I have an HTC Desire A8181...

Everything was working fine, until one day I turned off my unit then booted it back then it says "limited service"... I tried searching for network operators but the it will tell me "your sim card does not allow a connection to this network"...

here's what i have tried:

-resetting the unit to factory default
-rebooting the unit multiple times
-enabling/disabling airplane mode
-i have also tried downloading Anycut(app) - to view the phone info and to disable/enable radio
-tried changing network mode from WCDMA to GSM only
-turning the phone off and removing the battery for 30 mins.

but none of these worked, my phone is useless for a whole week now.
 

Re-seat (remove and re-insert) the SIM card?
Try a different SIM card?
And yes, check with O2 that they haven't blocked it.

Tried that multiple times, I also have used a different sim card.
I'm actually in Asia, and this is supposed to be an openline phone.
It was working a week ago, but now its just an MP3 player. If this can't be fixed I don't think I'll still be buying HTC phones in the future. 

I I had this and found it was the task manager auto.killing the operator service unchecked now ok .

After 2 long weeks, I finally got my phone back from repair. The technician told me that it was a problem with the mainboard and it has to be changed. So if you have tried everything and it still does not work, I suggest you bring it to the nearest HTC service center. They did a great job and I did'nt pay for anything. Sweet!