I've been having an interesting time with the Vista SP1 install and Virtual PC 2007. After installing Vista SP1, I thought all was well. Assuming "Well" means that you now have "For testing purposes only" and the build number watermarked in the corner, but I'll save that for another post.
I was unfortunately at a client site when I went to start Virtual PC 2007 for the first time, post Vista SP1. Started okay but then as soon as I clicked on "New", all I got was an open task in the task bar but no window on the desktop. Hovering over the task bar item, I could see that the windows was blank according to the Vista thumbnail view.
I tried uninstalling Virtual PC, getting the latest bits, reinstalling...no good. I posted a message on the MVP Vista boards and got a response from Paul Adare, MVP Virtual Machines. (Thanks Paul!) He mentioned that he has heard that this was reported and suggested:
"Try deleting C:\Users\<user_name>\AppData\Roaming\Microsoft\Virtual PC\options.xml and then starting VPC again."
That did the trick.
This is because the configuration is set to display the window in an area which is way out of the scope of the current viewable area. This may be due to switching between multiple dual monitor configurations and sleep mode?