Cannot delete windows partition from mac I want to remove Windows from Mac and the I know the simple way is through the Boot Camp Assistant. But that doesn't work for me as follows:



However, when I try to merge the partition of windows through disk utility, all buttons are inactive, and I cannot press either '-' or 'option' button, like follows:

 

Then, I try to reinstall a new Mac osX from the internet by pressing and holding the [command]+[alt]+[R] when starting the computer, and it doesn't work either. I am informed that the system cannot be installed in either the BOOTCAMP partition or Untitled partition since they are not GUID partition table format.

I am a newer to Mac and I just want to delete the Windows partition and add the space back to my osX partition. I wonder what should I do next? 

Thanks for help!
First of all, try both repair disk (if grayed, then verify), and repair disk permissions. If you are still unable, boot to single-user mode (Command +S  on boot) and type in the following.

/sbin/fsck -fy


Press enter, then type reboot.

If it still does not work, then do the following, but be sure to backup:

Hold Command +R  on boot to start Recovery mode, select disk utility and do it from there. If it is grayed out, select the partition scheme to 1 (or 2 if you need Untitled)



Warning: There have been reports that setting the partition scheme to 1 or 2 can erase all your data. Be sure to backup before attempting to do this.