Some Windows Vista users have experienced a problem viewing Gadgets. They sometimes appear as a blank black or white box. For some users, going to Java.com and downloading then reinstalling Java seems to work. If that doesn’t work, try the following steps.

1. Click Start > Run and type cmd.

2. Press Ctrl + Shift + Enter. (elevates rights)

3. Press Alt + C to close the User Account Control dialog.

4. Type cd c:\Program Files\Windows Sidebar

5. Type the following and press enter after each line.

regsvr32 -u sbdrop.dll
regsvr32 -u wlsrvc.dll
regsvr32 atl.dll
regsvr32 sbdrop.dll
regsvr32 wlsrvc.dll

See also:
Run a Command as Administrator from the Windows Vista Run box

Vista sidebar gadgets won’t view