After Parallels install, can't boot Windows in Bootcamp

1) I installed Windows 7 on a Boot Camp partition and everything was working perfectly.
2) I wanted the ability to access Windows while I was in Mac OS so I installed Parallels 9 and selected the option to use the existing Boot Camp partition. During the setup process there was a notification that Parallels was 'upgrading Boot Camp' or something similar.
3) Windows is working fine in Parallels however for heavy lifting stuff such as Autodesk Inventor I want to continue using Windows through the Boot Camp interface.
4) This is no longer possible. I don't get past the point where (after pressing the option key at startup) I choose Windows and press enter. It just hangs.
5) It's very frustrating and I am losing valuable working hours. I have tried deleting the pvm file in Documents/Parallels in the hope that I can go back to using Boot Camp only but unfortunately it no longer works.

Can any one help?