Nothing - it just blue-screened out of nowhere. I've done a full HDD test using TuffTest, then a low-level format - HDD had no probs. It just appeared that the HDD decided to allow the system to get corrupted: hence, my thinking that it could be a fault on the UPS. Another thought is that a USB device attached to the system periodically "glitches" it - I've seen that on some of the photo printers before, so perhaps my friends Epson photo printer is sending a "spike" p the USB?

Anyway, in the interim, I'd like to know how to fix this permissions glitch before I have to do a reformat. I've cloned the drive from an SATA to an ATA using Disc Wizard, so I'm no working off the original HDD...