PSU Issues

Got a brand new 600W power supply for my pc. Connected it up and u press the power button and it starts up for a second and then cuts out and i have to manually turn the power off then on for it to work again. Looks like the power supply is shorting out as when I connected my old 400W one back in it works fine so I dont think it is the motherboard/etc shorting out. Any other theories as to why it isnt working before I send it back for a new one?

What manufacturer is it? (Antec, Fortran, Enermax, Seasonic, Zalman, Thermaltake, etc…)

A warning about powersupplies: The rating given to a PSU (600W in your case) is practically meaningless. Read some of the following articles to understand why the above is true.

Some links to reviews and information:

Tech Report

Extreme Overclocking

Nordic Hardware

Brands I have heard good things about:
Antec (I use a True Power 480)
OCZ (expensive)
PC Power & Cooling (premium price, premium quality)