Press and hold the Sleep/Wake button and Volume Down button simultaneously for at least eight seconds or until the Apple logo appears. You may need to repeat this step.

If the above step 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. Try resetting the iPod while it is connected to power.

I had this very issue and spent six hours on the phone with Apple and they couldn't fix it ...but here is what I discovered and it worked to clear up the issue. First, see if the iPod works on a different computer without automatically going to "OK to Disconnect". If it doesn't, it may have issues. If it does, you need to perform a "Restore" (not a reset) on your 6th Gen Nano. This will wipe out any tunes on the iPod, but you said you don't like the ones on it anyway. Once the Restore is complete, first and foremost, tell it NOT to automatically sync to iTunes on the registration screen that pops up immediately after the restore by unchecking the related box. Then, be sure to Rename the iPod. That's the fix that worked for me, so hope you have the same results. For instructions on how to perform a Restore, go to www.apple.com/support and type in "Restore Nano 6th gen" in the Support page Search box in the upper right corner of the screen. That will bring up instructions on how to do the Restore. Good Luck!

omg omg omg omg thank you sooooooooooo much i was about a second from throwing my ipod mini out