I wish to delete Windows 8 and go back to Windows 7, which was originally installed. Having done the compatibility check for a Windows 7 installation it did not throw up a problem. However, on trying to install I got message error 0x0. I am happy to format the hard drive if that is what is needed.
One of my Win7 installs was similar but not exactly like yours, but I recall the option within the Windows 7 dvd installer to edit and/or format the partition(s) on the hard drive. This would be my suggestion based on what you're saying. There are "Live CD" options based on linux that include hard disk tools, not sure what your familiarity is with all that.