Ok, so I was validating the last C backup in Acronis True Image, while copying files with Roadkill's Unstoppable copier from C to S when all my open windows started freezing up, first with explorer, the weather channel, and that horlanger desktop clock. I did a hard reset, and everthing seems ok, S' raid array is being rechecked, with 4 parity errors, hopefully from the copy operation.