Just installed VS2010 express for Windows Phone last night. Install went smoothly. It creates a project, compiles, and deploys the app to the emulator.

Here's the problem: When I try to "Add Reference" through the Project menu, I do not get the Add Reference dialog box. Same thing if I right click References in the solution explorer and click Add Reference. That's not all. "File...Open" and "File...Open Project" also fail to throw up an open file dialog box. When attempting any of these actions, the IDE quickly loses and regains focus. Even pressing a keyboard shortcut (Ctrl+O) causes the IDE to quickly lose and regain focus, but no open file dialog box appears.

This is what I have tried, not particularly in this order:
1. Turned off UAC
2. Monitored file and registry access using Process Monitor during a File...Open operation. File activity showed mostly "SUCCESS" with a few "FAST IO DISALLOWED" and a few "INVALID DEVICE REQUEST" results. Registry activity showed mostly "SUCCESS" with some "NAME NOT FOUND" and a few "BUFFER OVERFLOW" results.
3. Created a new, clean Windows account to run the IDE from
4. Forced a test project to add a reference to "System.Xml.Linq" by editing the ".csproj" project file. Project failed to load in the IDE.

I don't have these problems at all on 2 other Windows 7 computers with VS2010 C# express beta 2 installed. One machine is 32bit and the other 64bit, both Home Premium edition.

My system: Windows 7 Home Premium, 64bit
Other Visual Studio products installed: VS2008 C# express, VS2008 C++ express

One other thing to note: Several months ago I installed the non-phone distribution of VS2010 C# express beta 2, and I had the same exact problems. Back then I chalked it up to being beta and went back to VS2008 C# express, where I do not have these issues.