Could you please share some more information to narrow down the issue.
1) Which version of Flash Player are you using?
2) Which browser are you using? What version of it? Is the issue specific to a particular browser?
3) share some particular video URL's for which green screen comes
4) share the dxdiag file of your machine. Type dxdiag in search of your computer. select the second tab "Display" in the window which appears. Now save the info