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#11
Did you try System Restore and compare the Services settings Defaults in the tutorial Shawn linked?
You may get enough relief from those three scans, but if there are irreparable System files and problems persist, then I'd consider the Repair Install which keeps your programs, files and settings in place and reinstalls the OS. Make sure to read over Shawn's steps closely as you'll need to have a readable Product Key on the COA sticker and there will be a few settings you may need to set back.
If your neighbor's installation disk doesn't work, how to obtain media for your licensed version is discussed in Step 1 of Clean Reinstall Windows 7 including how to unlock other versions from the same disk to make your own.