Recently when I accessed Windows 7 "Turn Windows Features on or off" (Control Panel -> Programs) option it just gave me a dialog box with a blank list. Normally you would get something like this:
But what I got was the same dialog box with a blank list. It displays "Please wait..." initially but the list doesn't appear afterwards. This is a problem known by Microsoft, but the solutions they have provided DON'T WORK!
I found this nice article mentioning the same problem and I fixed the problem according to the instructions given there. Visit FIX Blank or Empty List in Vista Turn Windows Features On or Off (OptionalFeatures.exe)
You have to download and run a tool from Microsoft and act according to the log it produces. Procedure is the same for Vista and Windows 7. Just make sure to download the correct version of that tool for your OS.