We normally say that re-installing is a last resort but it does have one major fact in it's favour- it's an opportunity to clear out all the crud particularly in the registry. Before we head down that road would you rather we tried some basic fixes first (although it sounds as if you've tried most of them) or do you want to jump straight in?
I clearly don't want to recommend spending any money but a 1.2gh processor ain't that fast these days. Have you increased the RAM lately?
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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.