Disappearing Text/buttons in Dialogue Boxes

All,
I have a dell inspiron desktop (530), with a intel core 2 duo and 1gb of
ram. It is running Vista Home Premium (32bit). No video card. Connected to a
Samsumg 22" WS monitor.
Here is what I am seeing:
When I start the computer, the dialogue boxes (for example, the System
Properties box where you change your computer name, advanced properties,
etc...) look fine with all options/buttons/text present.
After working on the computer for a few minutes if I access the same
dialogue boxes again, there will be random "missing" text/buttons!!!!

What could be causing this?

Any help would be much appreciated. I wish I could attach some screenshots.

Thank you!!!!