The correct command is sfc /scannow, with / in stead of a \ and a space before the /.
If no luck fixing this, it might be time for a reset or refresh. This can be done from inside Windows 10, usually. If not, make a disk or USB=-stick with the installer.
I recently upgraded to Windows 10. I wanted to change my username. But it won't let me change it. Or add a Microsoft account. I wanted to switch to a local user. I can't do that; I get error 0x80004005. I have tried a clean boot, but the clean boot does not work, just boots normally. I have tried sfc\scannow, does not work. It won't let me add a PIN either! Please help. I'm at my wit's end.