Ground drove my computer loopy.

So I've spent the last seven hours trying to get my desktop to boot something, anything, that's a full operating system. For much of the time, the system was hanging randomly between POST and loading the boot sector, and for much of the rest of the time, it was consistently hanging when I tried to load a Linux kernel. I even wound up going so far as to flash my BIOS, because I couldn't think of anything else to try that made any sort of sense.

The flash upgrade had gotten me to the point where I could at least load boot sectors again, and I was able to run memtest off of live CDs, but I couldn't seem to boot into 32-bit or 64-bit Linux, either my installed version or from a couple Xubuntu live CDs.

I was beginning to suspect some sort of weird flash corruption that was preventing me from using graphics card features, or possibly from switching to protected mode or x64 mode. (I don't know how memtest86+ works, as far as accessing all 8GB of my RAM. I'm pretty sure the BIOS is still in Real mode when it runs its initial sweep, but maybe it's bouncing back and forth between Real and Protected during POST.)

The thought of another outlay to continue having a nice computer at home was not appealing.

Finally, a few minutes ago, I realized something. I had two relatively new pieces of hardware attached to the computer: An APC UPS and a powered USB hub. I disconnected the USB connection between the UPS and the computer, and disconnected the hub, and rebooted the computer. The 32-bit Xubuntu live CD came right up. Huh. Reboot, throw in the 64-bit Xubuntu live CD, and *that* came right up. Huh.

I haven't tried booting off my hard disk yet, and I think that'll require some grub command-line magic to deal with device reordering stemming from the BIOS upgrade and CMOS changes. However, I think it's ultimately workable.

What I think happened is that the connection of the UPS and the powered hub to the computer via USB led to a ground loop that was messing with the internals of the USB controller on the motherboard. See, the powered hub isn't plugged into the UPS; it's a fair bit away from the computer, and I'll have to run an extension cord to get the UPS's power to it. As long as the operating system didn't try to do too much with that USB controller, things worked fine. That meant I could get into BIOS and tweak things, and it meant I could get into grub and memtest without too much trouble. Well, sortof. Remember how, before the flash upgrade, the system would hang at a random point between POST and loading the bootloader. I think the flash upgrade may have changed part of how it dealt with the USB controller, with the newer version inadvertently working around some of the ground-loop-induced weirdness.

So, yeah. A little more experience for those weird situations.