If you have a MinGW installation (e.g. in C:\MinGW), did you try renaming the folder? I tried and if I don't rename it, Code::Blocks automagically uses the compiler from my local MinGW but if I rename it, Code::Blocks says:
Execution of 'mingw32-g++.exe ...' failed.
Edit:
Looking at your "File Monitor" screenshot, it seems Code::Blocks opens "G:\CodeBlocks\mingw32-g++.exe". Since your Code::Blocks executable is located at "G:\CodeBlocks\codeblocks.exe" and your compiler directory is "$(codeblocks)\..\mingw", shouldn't it open "G:\mingw\bin\mingw32-g++.exe"?