My linksys e1200 cannot connect to the internet

First of all make sure that your demo is working fine and you are getting internet when you connect the computer directly to the mode.
If that is working properly then your router may need to reconfigure.
Press and hold the reset button on the router for 10 seconds. Release the reset button and unplug the power cable. wait 10 seconds. Plugin the power cable. Wait for 30 seconds.
Now reconfigure the router.
When you reset the router, it will come back to factory default settings and you will lose all the settings.

linksys e1200 setup

Reset and reconfigure.