Failing drives or a power supply that dipped out at the right time.
With 3 drives and what else, is that the stock power supply?
And are you ready for the drives to vanish? Backups all done?
New Gateway FX6801-01; primary hard drive working normally, two additional hard drives installed, and at least once a day, one of the two secondary hard drives 'disappears'! Reboot, and it's back. If I have only two drives, the primary drive is OK, and the other drive 'disappears'! Why am I 'losing' a hard drive from the system, 'sometimes'?