Hello,
I also had the same problem as described in first post.
I'm currently using Oracle VirtualBox which adds few bridges and network adapters.
I don't know what happens exactly, but disabling device: "Intel(R) Centrino(R) Wireless-N 2230 - VirtualBox Bridged Networking Driver Miniport" allows me to connect/see "add a wireless display".
For those of you who are interested you have to go to Device Manager and do View -> Show hiden devices to be able to see it.
When I have this device enabled windows seems to think that projector is already connected and for that reason won't connect to anything else.
It took me a few irritating moments to realise it.
I also had similar situation before I started to use a VirtualBox. Every now and then system was under the impression that it's already connected to projector. It feels like this fact should be easy to determine, but obviously not.
Currently every time I want to connect to my TV I have to disable that one device.
I wouldn't recommend using WIDI to anyone.