Qt Creator 2.6.2 and Qt 4.8.4: Qt version is not properly installed

Windows 7: I have installed Qt 4.8.4 Win and Qt Creator 2.6.2 Win, VS2010 (from here). When I try to open a project (previously compiled with Qt 4.8.3 / Creator 2.5.2), it says I need a kit (no valid kit) and eventually I end up at Qt version is not properly installed. All is shown in the screenshots below.

I have checked some solutions:

1. SO QT version is not properly installed, please run make install is for Linux
2. Some say, I need to install Qt SDK, but where do I find this (this one contains older Creator / Qt versions), and what sense would the individual installers make if I need SDK?
3. Some say, I need to add Qt to path, but what exactly? Creator? The Qt 4.8.4, the qmake dir?
4. Somehow I fail with this make install, nothing happens.
5. I have installed the 5.0.1 including Creator 2.6.2 as one installation, this works. But when I then download 4.8.4. and try to add it as QT Version, same issue: Qt version is not properly installed

Any idea what I would need to do or install.

— Edit — List of trials —

1. Added my Qt 4.8.4 and its qmake dir to PATH
2. Re-installed Qt in different order: Qt 4.8.4 first / Creator 2.6.2 thereafter
3. Opened Qt CMD Prompt qmake install (as in the suggestions): 4.8.4\install:1: Parse Error ('INSTALLING Qt Source Package Version 4.8.4.') Error processing project file: install
4. qmake install from Qt CMD. Runs 20 minutes, Laptop gets extremly hot, then it crashes

P:\Qt\Libs\4.8.4>qmake\qmake.exe install
QMAKESPEC has not been set, so configuration cannot be deduced.
Error processing project file: install