I need to write this down so that I can remember this blog post when it happens again.
Three days ago my Windows 7 installation was hanging on shut down. Safe mode worked. And as of today, I wasn't able to install or uninstall software anymore. The Windows Installer Service (msiexec) deadlocked right from the beginning. Another deadlock appeared when I wanted to disable or enable network connections. The event viewer showed nothing remarkable.
And I couldn't even use system restore anymore. The "Preparing to restore your system..." dialog never disappeared. And when I managed to restore an older system version from within the Safe Mode, the problem did not disappear either.
And what was it? Either my USB hub or some device connected to it was not working. Probably a USB device was temporarily malfunctioning, or the cables weren't connected properly. I can not even tell, because after I disconnected the hub and checked all devices and cables, everything worked again.