Once again: A Windows Installer Problem

Windows 7 Professional 64-bit, admin rights. Advanced user (many years experience in installing and working with and "inside" windows versions).

Ok, all started with problems installing a newer version of a NVidia graphics driver (196.xy). It stopped by saying that the control panel can't be installed and therefore the whole driver will not be installed and it will roll back to the last working driver. But I - as recommended by many people - had uninstalled the last one (195. xy) which had installed and uninstalled flawlessly. So my system went back to a driver Windows 7 brought with it (1.10 something).
After that also my old driver (195.xy) did not install - same error message. I tried a lot and at last I had to use a system restore point. I tried many things (safe mode, installing over the old driver, ...), my last hope was always the system restore point.

After that the problems began. I had difficulties installing things which use the Windows Installer. The error messages where almost always the same: The software cannot be installed as the Windows Installer Service could not be accessed (the service WAS running, as I checked under "services) as- for example - by installing the newest Java RTE Update 19 for 64-bit. I even cant uninstall older programms, as the uninstaller searches for MSI-files in temporary folders that were created when the programm were installed and later on (after the successful installation) deleted by the installer (as it should be, as I presume). I cannot update programmes to newer versions as the installer has to uninstall older versions and therefore seeks the temporary folders that do not exist anymore. Some newer versions of programmes I can install by putting the older version installer into the path it laid, when I installed it, but it does not work very often.

As there is STILL no version of the Windows Installer 5.0 downloadable in the internet (Thank you MS ), how can I fix my windows installer?

PS: Windows updates install - at least until that moment - without problems ...

That's correct, Installer Cleanup did not install very well (tried it before)... however: That does not solve my problem. I will try a repair install and report back - if I can

The Repair Insall seemed to work ... thanks.