Any combobox I try to open in the system closes itself instantly after having slided open. This makes it impossible to select something in a combobox. An example combobox is the one allowing you to choose the type of document (doc, docx, rtf) in the 'Save As...' dialog box in MS Word (or Notepad or ...). It looks a bit like the focus is gone (or stolen by something else). Trying to navigate the combobox with the keyboard results in the same behavior.
After several hours of research I've found a couple of people on the internet experiencing the same issue, but none have posted a solution.
The most comprehensive thread I've found is this one. It even has a video showing the exact same issue.
Own attempts to fix this:
The issue does NOT occur on a new (other) user account or when starting the computer in safe mode.
When using mconfig to disable all items on the 'startup' tab, the issue still occurs.
Changing keyboard and mouse to a spare one does not help either.
I would be most grateful if someone could help me out with this. If you want any more information; please ask!