I'm having same problem. It was working before I had friends over, whenever they left I tried to connect to the TV. It said it was connected but the TV screen was black. I found that if I switch to extended display it works fine.
I was using a Belkin Screencast adapter I assumed the problem was with the Screencast adapter so I purchased a Netgear Push2TV adapter. It behaves exactly the same.
I deleted the WiDi software, made certain all drivers etc. are up to date and re-installed the WiDi software. Same behavior. Again, it works fine on extended display.
It works fine if I connect to the TV using wired connection (VGA and sound cable)
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My computer is a Lenovo t520.
O.S. Windows 7 Home Premium
Intel(R) HD Graphics 3000 3/18/2013 Version: 9.17.10.3062
Intel(R) Centrino(R) Ultimate-N 6300 AGN 4/18/2013 Version: 5.7.0.3
Intel PROSet;Wireless Software 5/29/2013 Version: 15.8.0
Intel WiDi Version 4.0.18.0
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