After lots re-installations of Windows perhaps you have some difficulties with the file permissions on some old files.

To fix that all you have to do is to open a command promt as administrator and type the following:

icacls * /T /Q /C /RESET

That will reset the permissions and give all Users read/execute permissions to it.

Then you probably want your account to have full access:

icacls * /T /Q /C /INHERITANCE:e /GRANT YouUserNameHere:(OI)(CI)F

That will edit or remove (:e or :r) all the inheritance options - grant new ones  (IO and CI) - and give you Full (F) permissions. OI = object inherit, CI = container inherit.

The switches /T /Q /C are just some generic you always should use.