Anytime I had a problem running sfc it turned out my PC was badly infected. I think I even have a thread around here from the last time it happened (not that it would apply to you, my PC isn't a 64)
I use Advanced System Care right now. You can set the sfc to run from it on the next reboot but while it is doing it's scan to fix all the little shit before the reboot, it does a brief scan of the disk to look for errors then does the actual sfc on reboot. It 'may' be worth checking out. They have a free version of it HERE.
In the meantime or otherwise, my first instinct would be to run Malwarebytes and my anti-virus just to be safe.
*edit...just looking around, the first thing I came across from MS on this with W7 64-bit says -
There is a very good chance that you are seeing the effects of a hijackware infection! - post is HERE
Also - If you can boot into safe mode, try running the sfc from there.