I bought an MZ-RH910 and had the same problem almost immediately -- it died with the "no disc" error. The day it arrived, I made a series of recordings successfully using a mic, and played them back. No problem. Then later I put in a new disc and went out to a friend's concert, and recorded some of it as another test, again with microphones (Core Sound binaurals). After pressing stop, it got stuck in "data save" mode for several minutes, and thereafter I got the "no disc" error, no matter what disc I put in (including the one I had recorded on successfully earlier). The only thing I can think of that may have caused this problem -- not that it should have! -- was that I unplugged the mics during the "data save" process. Since you say that your error happened when you turned your computer on, this supports my hypothesis that the unit is somehow sensitive to changes in electrical levels or something like that -- in my case with the battery-powered mics, in your case with the USB power. Just a hypothesis; I'm far from an expert in these things. I returned mine for a new unit, and my new unit is working fine. But now I'm making sure not to unplug the mics until after the data is all saved! Ernst