Problem with removing partion on my mac

I have used bootcamp assistant and installed windows on my mac. Later when I decided to remove it I used bootcamp assistant to remove the partition which I created on my computer to install windows. For some reason after the bootcamp removal process was completed, my partition on the mac still did not go. When I restart my laptop (and press option key) the windows partition still remains. When I click on the windows partition it opens and says that there is some problem and the windows iso is missing and says that it cannot find it. So I am not able to use my windows partition. I am able to use my osx partition. When I go to bootcamp to remove the partition that option itself is not there. When I open bootcamp the window which would help me to set up windows on my computer is opening. So I am not able to remove the windows partition. Even disk utility is not finding the windows partition. So I can't even use diskutility to remove my windows partition. The worst part is this partition is occupying 40gb space of my memory. I am not able to utilize this nor am I able to remove this partition. So how do I go about removing the partition??