After I have upgraded the motherboard on my desktop, a few things got messed up, the most annoying of which was that Visual Studio 2008 has lost its XSD/Dataset editor. Opening a data set resulted in opening it as a text or XML, and when I right-clicked the XSD file and selected "Open With..." from the menu, the XSD editor was not there. Repairing and completely uninstalling and reinstalling VS 2008 did not help. After searching the web I found that some people have the same problem, but I found no solution for Visual Studio 2008. The solution that worked for me was described for the similar problem with Visual Studio 2005. I ran “devenv /resetsettings” and it didn't help. Then I ran “devenv /setup” and hallelujah: XSDs are opening again in the Design mode! To launch devenv you will need to start VS 2008 command prompt first.