Keeping it alive, here is a tip for you. This time we are going to see how we could deal with Windows 7 gadget related issues. You may notice, many of your gadgets will go blank with black squares without any reasons. After googling a while, we found the following fix. Unfortunately, this fix applies only to those users who have administrator privileges.

Close all your open gadgets (Which eventually kills the sidebar.exe process)
Fire up regedit and locate this key “[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\]”, delete it!
Right click on the desktop and start adding your favorite gadgets again. This must fix your sorrows (and gadgets)

A thread about this issue could be found here