Actually previously I was having Windows 7 Starter on my laptop which was installed on C drive, but somehow it got infected by virus which I was unable to remove. So I tried to install new OS on C drive but I was unable to do so. Then I tried to install new OS on the drive other than C and installed. But now I'm unable to format the C drive in which previous OS was there. Whenever I try to format C drive it is showing message window like this, "Windows cannot format this drive. Quit any disk utilities or other programs that are using this drive, and make sure that no window is displaying the contents of the drive. Then try formatting again
". I think old OS is still there. How can I remove the old OS from C drive? Please suggest!