Which version of Windows are you using and are you using an OEM machine where the version of Windows was preinstalled, or is your machine a custom built one ?
Run the sfc /scannow again and when it reports it is unable to repair some files, copy and paste the following command to the prompt -
findstr /c:"[SR]" %windir%\Logs\CBS\CBS.log > %userprofile%\Desktop\sfcdetails.txt
This will put an icon onto the desktop which when double clicked will open the CBS log in Notepad, which you can then copy and paste into the reply box.
Also download SFCFix.exe and run that -
http://www.majorgeeks.com/files/details/sfcfix.htmlThis can sometimes repair files that a sfc /scannow cannot, but will produce its own log, which you can also copy and paste into the reply box.
A chkdsk /f or /r cannot run from within Windows so you need to type y and press enter when prompted so that it can execute after the next reboot before Windows loads.
To view the chkdsk log, after the machine has rebooted, go Start - type eventvwr and press enter.
When Event Viewer opens, ensure Event Viewer (Local) is highlighted in the left pane - if it isn't then just click on it.
When it has read the data and you see Critical, Error etc. expand Windows Logs in the left pane - click on Application then on Action/Find in the menu bar.
If using Vista or later, type chkdsk or wininit into the Find box and press enter - if you are using XP - look for a Winlogon entry in the scrollable window and click on that.
Cancel the Find box if used and read the report in the lower scrollable window.
As well as whatever else it reports, look to see if it reports any KBs in bad sectors.
If it does then create a system image ASAP before the HDD finally fails.
You can also post its report by clicking on Copy/Copy details as text in the lower right pane then right click in the reply box and select Paste.