Hi liux43, OK, so i would try deleting the partition an re-creating it at the start of windows 7 setup.
It seems to me that the partition has become corrupted for some reason ( boot mgr error ) and when you install you then get ( no OS error! ).
Try setup again, but delete partition and recreate, when you have done this, if possible before continuing with setup, shutdown and restart, then begin setup again .
Try this and let us know how you get on, good luck :-)