I can't get my T420s to connect to my wireless network or Ethernet. I've tried doing so on several different networks with the same result. I've run the Lenovo diagnostics and all seems to be well with my wireless card, which is an Intel Centrino Ultimate-N 6300 AGN.
When running the Windows troubleshooter and when connected to Ethernet an error message appears:
"DNS server isn't responding"
When I tried to connect the laptop wirelessly the error message that pops up is:
"Windows can't communicate with the device or resource (primary DNS server)"
This issues oddly popped up after I installed the most recent Adobe Acrobat update, but I'm not sure if there is any real correlation. The two other computers in my house can connect to my home wireless network.
The latest software updates may not have been properly installed.
Try restoring the machine to the point just before the recent software(in this case, Adobe Acrobat) was installed.
An alternative is to uninstall the software, run a system update, and reconnecting.