Q: Hello. I updated my iPhone 4S to ios 7.1.1. And now it shows "no SIM card". This never happened before. How can I downgrade?

Hey User13579,

Thanks for using Apple Support Communities.

Follow these steps to attempt to resolve the issue.

iPhone: Troubleshooting No SIM

http://support.apple.com/kb/TS4148

1. Toggle Airplane mode On and Off.
2. Try turning iPhone off and then on again.
3. Check for a carrier settings update. Tap Settings > General > About. If an update is available, a prompt will appear.
4. Remove the SIM Card and verify that it is a valid, carrier-manufactured SIM. Also verify that it is not damaged, worn, or modified. Then reinsert it.
5. Restore the iPhone.

Have a nice day,

Mario