does scan say who did the test or have some sort of record for their test? sounds like you need to do the section 75 or w/e blogins mentioned... it's a weird situation...we have to assume you know how to and have done a good job of connecting all the cables from the psu, inserted the cpu correctly, etc...because it really doesn't make sense that scan would attempt to screw you on every front (ie sending back a mobo with bent pins initially, saying they tested it and found it to be working)... does gigabyte have a record of receiving your board for repair? surely they tested it?
Have you looked carefully at both the 24 pin and 4 or 8 pin motherboard power connectors, I had a problem where the pins had been pushed out just a little causing poor contact, (inside the connectors from the power supply) and my rig did the same thing.
Could be a huge number of things including a dodgy earth. I would remove the motherboard from the case, place it on it's box and hook everything up from there. All you need to connect is the cpu, cpu cooler, graphics card, memory and power. If it boots up out of the case then your hardware is fine.
I had this situation once with a pos msi neo plat. I had two different sets of ram, two cpus and two power supplies. Could not get the ******* to boot. Sent it back to my mate and it booted first time for him. I take it you have tried with a single stick of ram? No other ram to swap it for?
