I find dead camcorders to sometimes power up without the battery. No USB ever made any diff.
So pull the battery and try. And read this forum for the old common fix (hand thump).
I have a Samsung Camcorder SC-MX20C (about 2-3 years old) and I cannot turn get it to power up. I have connected it to my computer via the USB cable and not only does the computer not recognize it anymore, the orange charge light does not even come on. It appears completely dead. I had used it 3-4 months ago to playback some video with no issues. I hadn't noticed whether or not the battery was completely dead...that is a possibility.
If the battery is dead and unable to take a charge, would the camcorder still not power up anyways if I connected it to my laptop with the USB cable? Any ideas on why I can't turn the camcorder on?