1. That PSU is a quad rail reviewed at http://www.tomshardware.com/reviews/power-supply-silent-passive,3189-2.html
It would be too easy to overtax a rail and get odd reboots.

2. I can't tell if you installed the OS after the changes. Windows tends to crash on hardware changes.

It's one or the other from the story told. Too bad the PSU wasn't a single rail as there are enough Watts. You might be able to eek by unplugging what you can from the +12V connections. Unplug second drives, that Optical drive, what else?