No Cellular network after front panel display replacement.

Dear all

I recently changed my broken front panel LCD display of iphone 4S. The phone works fine and no operating issues. However my SIM is not detected. I tried following

1. Reset network settings: It did not help

2. While phone is ON, I removed the SIM tray but no error message of "No SIM card installed" appeared. So is the hardware damaged?

3. When I am turing location services ON, i do not see that in status bar too.

3. In Reset options, following options are in grey: Reset all settings, and Erase all content and settings. --> does that mean I have to update the iOS is the only choice? Right now I am on 6.1.2 and my iphone is JB.

Please kindly advise if you have any solutions.