I recently discovered an issue on my Windows 7 x64 system where double clicking text files (associated with TextPad) and Excel files (associated with Excel) took over 30 seconds to open the file.
A few forums on the Web suggested that the problem was that a program on my system may be blocking DDE messaging. In my case it turned out that Acronis TrueImage 2012 was the issue.
After uninstalling this bad boy I found that my file open timings returned to normal.