I'm having the same issue on my XPS 400. Blinking amber light and sometimes the display shows code 2 and sometimes 2 and 4. I've tried removing every connection and hooking them all back up 1 at a time. Nothing. Then I took a multimeter and found that the voltage from my PSU is completely off. Instead of the 12v, 5v and 3.3v I am showing 14.2v, 6.2v and 4.3v.
With that said, is it pretty much a sure thing that its my PSU is causing me issues? When the amber light blinks my computer still has all fans running, just doesn't boot up.