Q: sim card not valid even when it was used before

Hello rollins1924

Start with the troubleshooting in the article below for issues with your iPhone and it not reading the SIM card.

iPhone: Troubleshooting No SIM

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

If you encounter any of the above symptoms on your iPhone, try these steps to attempt to resolve the issue:

1. Update your iPhone to the latest version of iOS.
2. Toggle Airplane mode On and Off.
3. Try turning iPhone off and then on again.
4. Check for a carrier settings update. Tap Settings > General > About. If an update is available, a prompt will appear.
5. 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.
6. Restore the iPhone.

If you still are unable to resolve this issue, contact Apple support for further assistance.

Regards,

-Norm G.