I am sorry that I haven't been back to this thread a lot sooner.
Due to Easter the relevant shops around 'here' are closed, so for the moment I am unable to prove my conclusion, which is:
The problem is not inside the computer or inside the monitor, but outside! Yes, the problem is the cable between the pc and the monitor.
I am using the only cable I had that would fit the eh.. fitting, and it took me a long time (several days) to realize it merely is a so-called VGA cable, instead of a proper DVI cable. VGA doesn't do high definition, DVI will at least do the necessary 1920x1080.
With all relevant shops being closed for Easter, I have ordered a DVI cable to be delivered by snail-mail.
VGA (blue) and DVI (white):
will Win 10 not 'do' a 1920x1080 monitor?- these kind of cables will only transfer video, not audio.
Info:
monitor:
Viseo243D by Acer / packard bell, 24" / 61cm, 1920x1080 pixels. Made in 2014. Not Plug&Play. No loudspeakers.
"New" desktop tower: Gigabyte Technology, homemade 10 years ago: 2007.
64-bit, Intel Core 2 Duo. CPU: 6700 @ 2.66GHz, Intel P35C
Memory: DDR2. 8191MB=8GB RAM. However, SIW is reporting this to be wrong, incomplete values => sockets: 4x1024=4GB RAM. But every time I start the computer, the black&white loading page will say 8GB. I witnessed the technician try a lot of different memory sticks, before the PC would accept the 4x2GB solution.
No HDMI
Disk C: 1.8 TB
Disk D: 18GB
Windows Experience Index:
CPU score: 5.80, Memory score: 5.8, Graphics score: 2.0 (hence this thread!), D3D score: 9.9, Disk score: 5.9