I currently have 5 of the Elite Desktop 800 G3 that restart during the day or evening. I have updated all the drivers from the HP website. I ran the HP diagnostic app and ran all the test and they all passed. I tried to pull the CMOS battery and reset the BIOS as well as I read something similar on the forum about this issue which was close to what I am experiencing. I've putt all the PC's on UPS backups as well. I have swapped them out for newer HP PCs and the issue doesn't happen on the newer G5 or newer ones.