Suppose u want to hide your Drives From your Friends. So Here is the trick for this:-
1) Go to regedit, than navigate to:-
2) HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionPoliciesExplorer
3) Now in the right pane create a new DWORD item and name it NoDrives(it is case sensitive).
4) Now modify it's value and set it to 3FFFFFF (Hexadecimal).
5) Now restart your computer.
6) So, now when you click on My Computer, no drives will be shown.
To enable display of drives in My Computer, simply delete this DWORD item that you created.Again restart your computer.You can now see all the drives again.