3rd Party Gadgets Will Not Install

I have installed Windoes 7 and the Windows Sidebar has all the default Gadgets including Calendar, Clock, CPU Meter etc but I cannot install any others.

I have clicked on the "Get more gadgets online" link in the Windows Gadgets window, downloaded several gadgets including 'BlackCalendar.gadget', 'shutdown_v2.gadget' and 'DigitalWorldClock.gadget' but when I double click on them I get the "Do you want to open this file?" dialogue box, I click on OPEN and the Windows Gadget window opens which shows the nine default gadgets but the new gadget does not appear and nothing else happens?!

I have followed some suggested cures from various websites but without success.

Can anyone assist please?

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