I have windows XP. The scan disk does not work in normal mode or in safe mode, or from the cmd prompt (chkdsk). The message says the volume is being used by another process. The defragmenter does not work. The system restore does not work. All restore points are gone. Can not create a restore point. Antivirus program shows no virus or malware. No unusual processes in the system tray. I was infected a few weeks ago with something called Win Police Pro. The antivirus go rid of it but that is when I noticed the problem.

Maybe some help in this ---- http://support.microsoft.com/kb/555484 Unable to run CHKDSK

Problem is fixed. Problem was caused by Rootkit.tdss. This thing is nasty. This was left behind when Windows Police Pro malware was removed by the antivirus (Trend Micro). The rootkit was carefully concealed so the antivirus would not see it. The MalwareBytes software was able to remove it.