I guess you can redownload service pack and reinstall it.

来源: 于 2013-06-01 00:34:05 [博客] [旧帖] [给我悄悄话] 本文已被阅读：次

Before on windows xp, you can download service pack as an exe file, then run it to update service pack. You can probably do that on win 7 too. If your computer successfully reverting changes, then next time I do not think it will take long time to start.