I'm trying to use some MOV files my client provided, and they only play audio. I can't get video on any of my players either - on two systems. Is there a new codec out there?
Open them in Quicktime and check the properties. If they are encoded with Apple Pro Res you will need to download and install the Pro Res codec from Apple.
If they are FCP .mov files you may have trouble. One thing to try is the .mov to .mxf converter program from Convergent Design. (They're the people who make the NanoFlash, my favorite accessory.) http://www.convergent-design.com/
There's a link on their home page.
It's a free download and it's saved me more than once when I've had to move Final Cut files into a pc environment.