1. Try changing your color depth to 16 bit. It sounds like your card/and/or monitor cannot cope with the number of colors you are chicking at it. If that fails, try 256 colors.

2. Check the refresh frequency. If it is higher than 75Hz then this could be the trouble.

3. Clean the connectors! Seriously, this has fixed things for me in thepast.

4. Degauss the monitor - there should be a setting for this in the monitor setup buttons.

FM