Q: Ipad showing no sim afer insert sim card

Did you already reset the iPad by holding the sleep and home button for about 10sec, until the Apple logo comes back again?

iPad Wi-Fi + 3G only: If you can't access email or the web using the 3G network

Follow these steps, testing after each:

1. Check the cell signal indicator in the status bar at the top of the screen. If there are no bars, or if it says "No service," try moving to a different location. If you're indoors, try going outdoors or moving closer to a window.
2. Check to make sure you’re in an area with network coverage. Go to your carrier's website to see network coverage areas.
3. Make sure airplane mode isn't on. From the Home screen choose Settings, then turn Airplane mode off.
4. Turn iPad off and turn it on again. Press and hold the Sleep/Wake button on top of iPad for a few seconds, until a red slider appears. Then slide the slider. Then press and hold the Sleep/Wake button until the Apple logo appears.
5. There may be an issue with your wireless service. Call your carrier or go to your carrier's website.
6. Restore the iPad software. See Backing up, updating, and restoring your iPad software or see "Updating and Restoring iPad Software" in the iPad User Guide.

copied from iPad: Basic troubleshooting