After upgrading to Windows 10 Technical Preview Build 9926, I found myself unable to run the Windows Phone Emulator either from the Developer Power Tools or by executing a phone app from Visual Studio 2013.
I found a forum post online that showed how to resolve it. Here it is.
Open the Hyper-V Manager
Now click on Virtual Switch Manager on the right under Actions...
And then choose the Windows Phone Emulator Internal Switch from the list of switches and hit Remove. Don't worry, a new one will be automatically created for you the next time you try to connect to the emulator in Visual Studio.
Now launch Visual Studio as an administrator...
And try again to execute a Windows Phone project. The emulator took quite a while for me to open up, but it eventually did and worked great.
Hope this helps someone.