This is interesting. One of my PCs will only boot up when the Ethernet chord is not plugged into the computer. When it is plugged it, the fans will start up for a few seconds and then power down for a few seconds, and this cycle keeps repeating. Once I unplug the Ethernet cable, it will start up with no issues at all. I have tested this out numerous times at work, my house, and my parents house. The same thing at all three.