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The problem you are having sounds like the monitor is improperly configured. When you say "my Mac" is sliding and flashing, I presume you mean the various images are sliding and flashing. If you have the improper resolution, the improper scanning frequency, the improper refresh rate, etc., this type of behavior will be evidenced.
Make sure that you have set up the monitor correctly. This will eliminate all such problems and guarantee a stable screen image.