This restriction prevents users from My Computer or the Windows Explorer to access the contents of selected drives.Also they will not be able to use Run,Map Network Drive,or the "Dir" command to view the directories on these drives.
Type "regedit" and navigate to :
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\
Policies\Explorer
And to:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\
Policies\Explorer
Create a new DWORD in both these locations called "NoViewOnDrive".Add these decimals numbers to hide the drive(s).
A:1,B:2,C:4,D:8,E:16,F:32,G:64,H:128,I:256,J:512,K:1024,All Drives:67108863
For example,to hide drive A and drive C,you would add 1(for A)+4(for C) to get 5, and the value of NoViewOnDrive should be set to 5.To disable all the drives,set the value to 67108863.
You'll need to restart Windows to see the effect take place.
Note: Back up the whole registry and then apply the above hack so that if some thing goes wrong you can get to the old state.