NO SERVICE FOR HTC S710E . How do i diagnose the problem?

HTC Windows Phone 8x: Need User Manual:

Hello. Your User Manual for the HTC Windows Phone 8x has different User Interface for different Cellular Carrier Service Providers...

A little more information is needed to properly diagnose.

Assuming that your service is current and the phone has not sustained any recent trauma (such as hard impacts or water damage,) check and make sure the phone is not in "airplane mode." This would disable any signal coming to or from your phone.
Second, turn the phone off, remove the battery, wait a couple of minutes, put it back together and reboot.
If that fails, I would back up all of your contacts, photos, ect... and download the latest firmware for your phone from the HTC website. This will do a complete wipe of your phone and return to factory settings.

google : htc service centers

it will bring most nearly available service center.

Hi, you can use the following unlocking service (all HTC models are supported): http://www.fastgsm.com/en/htc/htc/desire/unlock-code

ASSURE CARRIER AND APN SETTINGS ARE CORRECT

It would be best to bring your phone to diagnose the problem. It could be a number of things, from software to hardware, so your best bet is to bring the unit to a service technician

To find your nearest HTC service locations, please contact to HTC Customer Service hotline at 1800-113377 from Mon – Sat, 9:30 am - 5:30 pm.
o2 is also known as htc prophet, o2 is htc make.

why don't you try www.247servicecenterinfo.com, they have listing of all htc service centers in india.

Click on the link below to choose your nearest service center and click on it to get the contact info.
http://www.247servicecenterinfo.com/index.php?page=mylinks&op=showCategory&id=54&title=HTC
You can also call HTC India customer support at 1800-113-377 for more details.