Why do the commercials play well, but when the video starts, I get green screen?

The videos and commercials are mostly likely encoded differently.  The green screen is symptomatic of a video decoding failure.  This is typically related to hardware video acceleration and the graphics drivers on your system.

Please work through the video troubleshooting guide.

https://helpx.adobe.com/flash-player/kb/video-playback-issues.html

If you're still stuck, please follow the directions in the guide on providing the dxdiag report and additional information about what you tested and saw.