Sounds like there might be a corrupted file in that last transfer.
If you connect in MSC mode, you can see if there might be a filesystem error. At the least, you can recharge the device.
First, try a soft reset. Press and hold the top power button for about 30 seconds, release, then try powering up as usual. This will restart the player. it’s possible you simply ran into a glitch. Once it powers up, check the battery icon to see if it needs a recharge first.
If it doesn’t respond, reset once more, but don’t power up. Press and hold the Volume Down button while plugging into the computer USB port. This will force a manual MSC connection, and the device can be reharged if left plugged in. Does the Connected screen appear on the device after a brief delay?
Once connected, you can select the Fuze+ as a basic flash drive. Right click on the device in Windows Explorer, and select Properties, then the Tools tab. Check the volume for errors under Tools. This will hopefully clear the error that might have occurred in that last transfer.
Again, after charging for a while, see if the device behaves normally after disconnect. There will be a brief delay, about 10 seconds, then the device should power up and do a database refresh. If it freezes during this process, it’s most likely cause is a corrupted music file, or one file that is hanging up the device.
Let me know what you find, and I can walk you through the issue a little further.