My ipod nano no longer powers on with the gpx radio w/ ipod dock

Push menu and the middle button and if its on hold turn hold off. and plug it into th ecomputer

Have you already attempted to reset the iPod? If not I would recommend doing so now. I've posted a step by step solution below just in case you need the information. Please let me know if this does not resolve the issue.
Toggle the Hold switch on and off. (Slide it to Hold, then turn it off again.) Press and hold the Menu and Center (Select) buttons simultaneously until the Apple logo appears, about 6 to 8 seconds. You may need to repeat this step. Tip: If you are having difficulty resetting your iPod, set it on a flat surface. Make sure the finger pressing the Select button is not touching any part of the click wheel. Also make sure that you are pressing the Menu button toward the outside of the click wheel, and not near the center.
If the above steps did not work, try connecting iPod to a power adapter and plug the power adapter into an electrical outlet, or connect iPod to your computer. Make sure the computer is turned on and isn't set to go to sleep.

If you are still unable to reset your iPod, use only one finger from one hand to press the Center (Select) button, and one finger from the other hand to press the Menu button.
When you reset iPod all your music and files are saved, but some customized settings may be lost. Date and time are preserved (unless the iPod reset itself because it had no power and then was reconnected to power). Other customized settings, such as Bookmarks, On-The-Go Playlists, Shuffle, Backlight timer, and so forth are preserved from the last time the hard drive turned on.

if you have updated the ipod scince, then that could be why - Revert it back to your old OS version, Or, reformat (save all your music on your ipod first) and try it that way. Or you could just charge it via computer?