Start Up Power Problems, Maybe power supply? Options

[PhatDesignz]

My Xbox is starting to act funny now and I am trying to figure if anyone else has had the same problem and what steps they took to correct it. The xbox will power on but turn right back off. When I don't have the A/V cable connected it will turn on sometimes and just flash green/amber. After I let it run for a few moments to make sure it won't cut out I then plug in the A/V wires and then it instantly shuts off. I have noticed sometimes when the A/V is pluged in on start up the box starts it normal start up with the flubber but then kills. I will order the parts I need but I am just wondering what parts I need. A new power supply maybe? The mobo and all is acting right if it will load to the bios fine but it seems soon as I plug in the A/V the power just kills. This is an un-opened box. Still all factory. Any ideas. Thanx in advance