Solved: ASUS P8Z68-V PRO GEN3 mainboard resetting instead of booting first device

I recently upgraded my main computer to a new shiny Intel Z68-based motherboard with a 2nd generation Core i7. A really nice piece of hardware, I'd say.

But while I was setting it up I had some very odd problem. When I plugged everything in and wanted to boot it, it just didn't want to boot any devices (but the EFI BIOS loaded without problems), it reset instead.

At first I thought I had a power problem, so I went out and bought a bigger PSU. But it still reset instead of booting. Then I called a friend and he thought the SATA controller might be busted. So he suggested unplugging everything and trying one part at the time.

After doing a lot of cross-testing I figured out that it was the USB cable to my APC Smart-UPS 1000 that stopped the boot from processing. So obviously either my UPS or motherboard firmware is incompatible with each other. Luckily I was not dependent on having the UPS USB cable connected, so I just disconnected it to avoid the problem. With that component disconnected everything worked as expected.

Moral of the story: Test with one component at the time if you're experiencing difficulties.