You should have programs that came with the grapics card,
and these programs are used for settings of the screen.
That is the first place I would look.
Rightclick on desktop, choose properties.
Then settings, advanced,
that should take you into the settings for your graphics card.
Cousin Roger ....
These types of adjustments may not be possible
on machines where replacement monitors are installed
in place of the originals and the original software
used to adjust the monitor properties is no longer
available ....
I have two 1999 vintage Compaq Presario machines
that are currently in that state ....
One replacement monitor that I use on a dual-boot machine
between Debian Linux & Win98 works almost perfectly
and screen adjustments are made from the buttons
on the front of the monitor itself ....
The other machine which I inherited a few months back
from a friend runs Win2K and the replacement monitor
is itself also old and is OK except for the brightness level
which is much too dark ....
The brightness level on the monitor itself will not render it
to a level that is really acceptable for viewing images
although menus and general text display is OK ....
Neither of the machines now have adjustments available
through the Windows Display Advanced Properties although
the Win98 machine did8 when it had the original Compaq monitor
and software installed ....
Both monitors have the correct drivers
for their specific models installed ....
I've searched the manufacturer's site for software
that is related to the monitor that I have on the
Win2k machine that is too dim but apparently they
no longer support it since it's too old, like me ....