Mahara isn't officially supported on Windows and I personally have almost zero experience with it, but the first things I can think of to try and debug this are:
- Is there anything in the error log? On linux this is usually somewhere like /var/log/apache(2)/error.log , I don't know where it goes on Windows.
- Do you have any weird javascript settings in your browser?
- What browser are you using?
- Is your session directory writeable? When it redirects you back to the login page are you logged OUT again? If that's the case, the problem is almost certainly that Mahara cannot write session files. Mahara puts session data inside its dataroot directory.
Maybe that's a starting point :)