I have been having issue with starting up my mac pro. I went ahead and pulled three drives and the system worked for 2 months. Yesterday it died again. I pulled the graphics card, replaced it with a spare. I pulled the ram, reseated it. I pulled the OSX HD sled, and than plugged it into a different HD slot. I have tried plugging the system into a different wall socket. I have not tried pulling my unused esata card for my unused external drive. I do not use the PCI esata card but it is seated. How do I know if it i smy power supply. Can I determine that myself? Or what else should I test? Thanks for your input. Here is a video, turn up the volume so you can hear the system turn on and off. http://youtu.be/i9RGaa55Gt0 Thanks!