No boot up.

When I press the power button the power on and reset leds flash, then nothing. With the case off I can see a surface mounted yellow led illuminated and a surface mounted red led illuminates when I press the power button. I'm guessing the psu is faulty but have not be able to turn it on using a connection between pin 8 and ground of the atx 20 pin connector with both the atx 4 pin and the 20 pin connectors disconnected from the mobo (in fact with all the connectors disconnected from the computer).

So psu or mobo?