To prohibit or disallow installation of new gadgets on the desktop in Microsoft Windows 7, you must register a restriction in the registry.
The message “Installation of desktop gadgets is managed by your system administrator” will then appear on the desktop, specifying the restriction.
As always, before any registry tweak, it is suggested to create a manual backup of the registry.
Steps:
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1. Click Start -> in the search field -> type “regedit” and confirm with Enter. Accept the security prompt:

2. Go to HKEY_CURRENT_USER > Software > Microsoft > Windows > CurrentVersion > Policies .
3. Right click on Policies ->Create a New key-> name the Key as Windows
4. Right click on Windows ->Create a New sub key-> name the Key as Sidebar ; while the Sidebar is selected, right-click anywhere in the right pane -> select New -> create a DWORD 32-bit :
(Click the screenshot to see it in full size)
5. Name the new value as TurnOffUserInstalledGadgets and double click it to set is value to 00000001. (Easy cheat for newbies: hold the “0” key until it fills, delete the last zero and type one. There are 7 zeros and total 8 digits).
8. Close the Registry Editor and restart the PC.
9. When installing new gadgets, the message
The installation of gadgets is managed by your system administrator
will appear on the desktop.
To remove the restriction, assign all zero (00000000) as the value data to TurnOffUserInstalledGadgets.