I suggest using either TDM's installer
http://tdm-gcc.tdragon.net/, or the C::B installer, that include MinGW (it's the one with mingw in the name).
If you install MinGW in any directory other than x:\MinGW (where x is
any drive), like C::B's installer does, you have to remove all x:\MingW directories, or you will run into trouble sooner or later.
After that yoiu should try to autodetect the installation-directory again (in Toolchain executables), if it does not work, you have to set it manually and make sure all exe's exist.