Hi buttoni:
It looks like what I did wrong was to disable Avast during the install of Ewido 4.0.
My rationale for doing this is that it wouldn't hurt, and I thought I had read something about Ewido's guard not wanting to be 'disturbed' during installation.
Just to be on the 'safe' side I turned Avast off because I knew that the guard would be installed either I wanted it or not.
But a boot and turning Avast back on was a real blackout for my machine.
It had been interesting to repeat the whole process with Avast on, to get confirmed that something on my machine doesn't like Ewidos guard.
The strange thing is that this happened twice, and just when activating Avast' Standard shield
both times.
Eweything is fine now and works as wanted.
Thanks for your interest.