Try this 1
Click on Start ---> Run ---> Type regedt32 and press Enter.
(If you are using Windows Vista or 7 then click on Start --> In search box, type
regedt32 and press Enter.)
"Registry Editor" will be opened.
First backup your registry by going to "File --> Export".
Now navigate to the below location.
Now click on "Shell"
At the right side there will be a file "Default". It's value should be "none".
If its not set to "none", then double click on default and type none --> Click on OK