Though OP is asking about Windows, this error also occurs on Ubuntu Linux and Google lists this result first when you search for the error"QtCreator: No valid kits found".
On Ubuntu this is solved by running:
For Qt5:
sudo apt-get install qt5-default
For Qt4:
sudo apt-get install qt4-dev-tools libqt4-dev libqt4-core libqt4-gui
This question is answered here and here, though those entries are less SEO-friendly...