I can no longer view posted videos. Any idea what might be causing this?

Try a different browser, firefox or chrome.

I never had a problem with it until lately. Other forums I participate in are not a problem either, so I am hesitant to change browsers to fix something only showing up with this forum.

You could try clearing your cookies on this site by clicking on the drop box next to my stuff or you can set windows media player as your default video program on your computer.