Tried, but still crashing Excel. As said, many of these hints are not
related to my problem.

For instance the one you point to is about:
"The reason for your crash is a problem with media previews in
explorer (explorer calculates a thumbnail view of an image or the
first frame of a video file). By disabling this feature (which is
useless anyway) explorer stops crashing."
But I am not using explorer (but Excel with VBA in xla) and I am not
using media previews...

As said, it looks that the error I got is also found in many other
instances, that is why I hope someone has really experience with
Excel, VBA and xla  and this error and how to solve it.

I googled the web, but could not find a link with these three things
in it.
Of course I tried others things that perhaps might do it (like yours
and many others things; I removed several programs from my computer
but no real help), did hijackthis (but can't really interpreate the
results. It does not look bad...

But perhaps someone can help me if something is wrong (see below).

> If that does not work there are 407 other answers you could look at.

Some advice is to clean my disk and install all applications. That are
nice advices of course (I see too many of them; even for simpler
problems), so I hope there is a less dramatic method available.