UAC (User Account Control) is a feature introduced in Windows Vista to prevent the execution of unauthorized programs from executing on Windows .This feature has been adapted in a different style in Windows 7 . In Windows 7 , you can’t access Sidebar and Gadgets when UAC is disabled by slide bar.
So this security settings would block anyone from installing a Malicious sidebar widget without user intervention . But many people who already disabled UAC is looking for a method to access those sidebar gadgets .

Enable  Windows sidebar and Gadgets when UAC is disabled .

Press Win+RUN and enter regedit .
Now this will open Windows 7 registry editor .

From the left pane , search for the following registration entry .

HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionSidebarSettings

At this point , move on to right pane . Right click anywhere and select to create a new DWORD of 32 bit value and name AllowElevatedProcess . Here set the value as 1 .

Now you can enable Windows sidebar and Gadgets when UAC is disabled .

You ca automate the process by the following registration entry .

Copy the following settings into notepad and save it as AllowElevatedProcess.reg

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionSidebarSettings]"SidebarDockedPartsOrder"="0x1,0x2,0x3,0x4""AllowElevatedProcess"=dword:00000001

Now run AllowElevatedProcess.reg with administrative privileges .

Now right click anywhere on desktop and see if you can enable add desktop gadgets .