In Windows XP and Vista there is something called System Restore which you can use to roll back your PC to an earlier date. However, it isn't fool proof and may not give you the results you want. Two questions spring to mind - (1) why didn't you listen to your expert and (2) what was this thing you clicked?
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Do you know that we're all in line for succession to the throne? Really?
Well, if forty-eight million, two hundred thousand, seven hundred and one people died I'd be Queen.