I believe that happens when Norton Antivirus deletes infected dll's in system 32 folder, and Windows fails to automatically restore them like it usually does so you must do it manually.
Go to
http://www.dll-files.com and get these dll's (some you might not need)
msxml2.dll
msxml2r.dll
msxml3.dll
msxml3a.dll
msxml3r.dll
msxml4.dll
msxml4r.dll
dfrgres.dll
dfrgsnap.dll
dfrgui.dll
Drag these dll's in C:\Windows\System32.
Try one dll at a time until you can succesfully open device manager.
You can back up your old dll's if you wish but when you put the new ones in then delete them windows will automatically start replacing them.