Considering all that you've tried, it might be time to do a repair install. It should preserve your user accounts, data, programs, system drivers, etc. I seems like there's a deeper operating system problem than system file checker can fix.
You would need an official installation disk, not a manufacturer's recovery disk. If you don't have one you could download an official iso file from Digital River and burn it to a DVD. It would have to be the same version of Windows 7 that's currently on your machine as well as the same bit-ness (32 bit or 64 bit.)
Official Windows 7 SP1 ISO from Digital River « My Digital Life