My 1.0 xbox simply won't power up any more, I have taken out the mod chip, tried it with ever possible combination of hooking up DVD or HD or neither or both. Tried my original HD and new HD. Whenever I press the power button it just "pulses" the power on. The network led light goes on and off and the nvidia fans starts then stops. Nothing else. The exhaust fan does nothing. Is the PSU dead? Any test that I can do with a multimeter would be great to know about. Thanks.

strange i have the same problem... i had my system modded for 6 months and it worked good, i flashed my TSOp and it worked for an hour then i rebooted for the 10th time and now I get the same problem your having ... someone help plesae

learn anything??

I don't think this is the power supply, I have the same problem (started after I drilled holes in my motherboard ). I've just bought a new motherboard to replace it, I'll tell you whether the new works when I get it. Then we'll know whether it's the motherboard or not.