Visual Studio just went schizophrenic on me: F5 started running File/Open/File, rather than Debug/Start Debugging; F9 refused to toggle breakpoints; and, none of the other default keyboard shortcuts appeared to be working normally. It took me a while to find the resolution to the problem. So, I'm blogging it for posterity.
In a Visual Studio Command Prompt, enter the following commands:
This command clears out your recent projects list, dumps your RSS feed, and more. It will execute for several seconds (perhaps even a minute), then return control to the command prompt. (Interestingly, the /resetuserdata switch does not appear to be documented – either in the command line help, or on MSDN. I found it on a blog.)
This command starts Visual Studio. Go ahead and close Visual Studio.
This command starts Visual Studio again, and allows you to choose your development environment defaults.
These commands did the trick for me in Visual Studio 2008. I believe they would also work with Visual Studio 2005, but I have not confirmed this.