Probably a long shot but can you open system restore.
The fact that sfc /scannow doesn't work suggests major problems, as does the fact various programs will not load.
If you look in control panel (classic view) and look at installed programs do you see anything you don't recognise ?
I'm no expert on this but have you tried booting into "safe mode". Can you download and install this,
I fear a reinstall may be the best option... save all your personal stuff to USB/Flash memory (if it will it let you do that)