HELP C:\ Drive got switched and programs don't work anymore

My uncle was trying to install drivers to a hard drive he had just purchased using my PC and afterwards he had a problem and we had to do a repair on windows (the repair that overwrites the old windows).

Even though the repair was on the C:\ drive it ended up on the F:\ drive (everything is still installed under C:\ so no programs work).

Anyone have any ideas on how to fix? I did the windows overwrite repair 3 times and every time chose C:\WINDOWS

Thanks,
Flash-matic :dog: