When you have the Plextor MediaX media HD (model PX-MX1000L) and you want to connect it to your PC as external HD with the USB cable included in the box, it could be that your PC doesn't recognize the Media HD. 

There's only one solution, change the USB cable.  The cable included in the box is from low quality.  Taking a good USB cable will solve your problem and your Media HD is recognized by windows.

it's a shame of Plextor to include such a bad quality USB cable.  The cable even doesn't work with other HD's.