If you get any other similar events, post back, with as much detail as possible, including any odd behavior you may have experienced in the previous use, and what software you've installed. I would suggest that since you switched power off at the wall before rebooting, it would be wise to check you didn't inadvertently damage the drive's data structure or directories - not likely, but possible if the drive was attempting to write at the time, and then do an SMC reset. An SMC reset was done and it has not happened again - though it may be purely coincidental that it hasn't happened again. I don't think there's been a clear reason found for this happening, and there is certainly not one from your description of this specific incident, but among the users I have who run Intel minis, I have had one where a boot failure occurred - the power light failed to light, though the chime was present and the system commenced startup then kernel panicked. The experience you've had with your mini isn't a common one, but it has been reported from time to time, so it's not unheard of.
