There might be two things you could try to get your system working. Running a chkdsk and System file check, never hurt. To run the System File Check, open an Administrative command prompt and type SFC /scannow. Maybe it will replace some files that have been damaged or corrupted.
Chkdsk might help clear up any drive corruption, if that is involved.
But if you have Windows 7 SP1, you can download a like version from online and then do an inplace upgrade which refreshes your system and leaves your personal files in tack. Of course not 100% reliable, so back up first.
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Since I don't have any systems with an OEM install, I may not be aware of restrictions in place when updating an OEM install due...