yeah, mince does it often, especially if you are using P2P or transferring a lot of files.
unplug and leave unplugged for 30 secs, then plug it back in, you may have to press the power button once re plugged.
If this does not to it a reset will be needed, with the little button on the back.
Must admit, now I use it a lot, I wish I'd gone for something else to be honest, the firmware is very temperamental.