It might be a driver issue, perhaps a conflict between two different devices. I have yet to this day to get my Sony 950 to work with my Windows 7 desktop although my 350 works fine. The 950 does work with my Windows XP netbook.

Concerning the nookcolor, I notice that I have to sometimes jiggle (very cautiously) the micro-USB cable before the light comes on to show it is charging. Remember that you have to use the supplied cable with the extra long micro-USB plug before the unit will show it is charging. It will trickle charge with a standard micro-USB and connect to a computer with a standard micro-USB cable , but won't indicate that it is charging.

Try a different cable with the computer. Also try using a different USB port on your computer. I would not use a USB hub as they are finicky. Try a different computer if you have one.