PSU is OK
How has this been determined? Without specialist equipment and knowledge the average computer user cannot test a PSU conclusively, check the guidance of Digerati
regarding testing a PSU @ http://www.geekstogo...-a-psu-problem/
other possible causes for this type of issue include overheating due to a failed CPU fan and the system (including the MB) shorting out as examples.
...I have removed all cards
Does this include the Ram? If not then remove the Ram and power on, what if anything happens, if nothing you should try bench testing the MB outside of the case, see my canned text "how to" below
Best couple of suggestions I can make would be first remove the MB and do a barebones set-up on a piece of cardboard (make sure it is larger than the MB) only connect the PSU, the GFX card, 1 stick of Ram and the keyboard.
You will then need to short out the 2 power on pins on the MB header to get the PSU to activate, you can use a small flat bladed screwdriver or a paper clip bent into a U shape, this is perfectly safe if you do not touch anything else, the idea is to see if we can get a BIOS screen if you do you can then add one component at a time until you find the problem component, you must power down and remove the power cord from the wall before adding a component, second suggestion try a known working PSU, it is not unknown for new components to be bad, third suggestion try and loan an ordinary PCI graphics card (not pci-e) again to try and get a BIOS screen.
Other things worth checking include, if you used stand offs beneath the MB are they in the correct locations (only where there is a screw hole in the MB) otherwise the MB will short out, check for stray screws or bared wires for the same reason, make sure the jumper cap that can be used for clearing the CMOS is not missing or on the wrong pins.
What is the brand and model of the present PSU?