<>
If your screen is flickering during gameplay, it sounds to me like a refresh rate problem. Refresh rate is how often the picture is "redrawn" on your monitor. Your monitor has an "ideal" refresh rate and using one too high could damage your monitor, so check. You can adjust the refresh rate in the display properties. I recommend something above 75mHz or so. (i play at 85mHz.)
what are your PC details? I may be able to help you with more information; assuming the suggestions so far haven't resolved your problem.
Glad to help,
<> Major MaNiaCaL
~*81st*~ Krewsaderz