When I had a problem that would not install certain updates on W7, not SP1. I was told by MS technet to do a repair install of W7, this worked for me. However one caveat. it took a long time (4 hours Plus) to do this, because you then must install all updates, but in your case you would need only to install SP1 and any updates that occurred after SP1. I also had to re-activate a couple of programs after the repair install.
Here is instructions for doing a repair install
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