When the correct screen resolution (screen area) or the right number of
colors are not available choices in display properties, settings tab,
then it is a good bet you do not have the right driver installed for
your display adapter.  The display adapter in your PC is either a video
card or a display chipset on the motherboard.

If you received a CD or floppy disks with drivers along with your PC,
see if they contain a display adapter driver and install it using:
control panel, system, device manager, display adapter.

If you know what display adapter your PC has but you have no disks, use
www.google.com to track down the correct driver on the internet.

If you do not know what display adapter your PC uses, you can go to a
MS-DOS prompt and type:  Debug       and hit enter.  The screen will
display a flashing prompt next to a - sign.  Type:  DC000:35 (DC000:50
may also work) and hit enter.  The name and possibly model of your
display adapter should appear on the right hand side of the screen.  To
quit Debug, type Q and hit enter.  If Debug is not helpful, you will
have to remove the computer case.  Look at where the monitor plugs into
the back of the case and then check that location inside the case.  If
there is a card there, you obviously have a video card and if not, you
have on board graphics.  Write down any information displayed on either
the card or the chipset on the motherboard.  Then use www.google.com to
search for the information.  Do not include all the data you found in
one search message--search on each piece individually.  If you include
all the information at once, you might not get a hit.

I have found that a video card will generally have to be removed in
order to see the information.  Be careful of static electricity as it
can fry components.  Before touching anything in the computer case (the
cord is unplugged, right?), ground yourself to the case by touching it.
Don't work on carpeting since shuffling your feet on it can generate
static electricity after you grounded yourself.  Remove the one screw
that holds the card in place and using a rocking motion (left to right
and back)to pull the card straight out.

Once you have the right driver, install it through control panel,
system, device manager or through control panel, add new hardware, as
appropriate.