If I understand it correctly the OP has a problem starting C::B.
And while starting we call in fact the standard compiler (compilerMINGW.cpp:368) to determine the version-string.
I can not see if something wents wrong here, but instead of only removing the MiNG's path from environment, I suggest renaming the folder MinGW resides in, because C::B executes the gcc in the compiler's masterpath.
Another possibility would be to rename C::B's config-folder (the one where default.conf is in, don't know the vista path at the moment, because I'm on linux), to see if it works then.