Yes..... perform an in place upgrade / repair as described here
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Make sure first that you have a legitimate product key and then obtain the proper installation media from here
If you have SP1 installed on your Windows 7 Machine
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If you don't have SP1 installed on your Windows 7 Machine
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I've had to do this a few times lately.... same deal helping friends.
You'll have tons of updates after the repair, but at least you'll be able to get them.
This procedure is generally non-destructive, so your programs, drivers, etc., should remain intact and without issue. However:
Nothing is 100% foolproof, especially to a determined and dedicated fool, so make sure you back up all critical...