I've seen this a few times, and I've never figured it out.
When I type cmd into the Search Programs and Files box and hit CTRL-SHIFT-ENTER, instead of getting an elevated prompt I get an explorer Windows showing c:\windows\system32.
Interestingly enough, if I right click on the Firefox button on the task bar and select "Open Private Window" the same thing happens.
SFC comes up clean, and the computer has been scanned for infections. I've seen this on several computers, mostly Win7, but sometimes Vista.
Anyone ever see this and know a solution? T
