sorry to hear you are having issues with your PC.
It is possible that it is the PSU but the paper clip test is not conclusive.
Remove the HDD and test it as described @ http://www.smpspower...rs-pinouts.html
Other possible causes may include a loose connection a memory or add on card come loose or even a keyboard error, open the case and check all internal components are securely seated or connected and be sure to disconnect the power cord from the wall first and observe anti static precautions before reaching inside, you can do this by touching a bare metal part of the case, if this does not resolve the issue follow the procedure 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, 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.
Keep us posted on your progress or let us know if we can assist with anything, what is the brand and model of the present PSU please.