So I bought some parts and built a new PC. This includes:
i5-3570k (with an aftermarket cooler)
2x4GB Ripjaws DDR3-1600
GV-R787OC-2GD (it is a Gigabyte Radeon HD 7870 OC with 2GB DDR5)
650W Cooler Master PSU
1.5TB Seagate Barracuda Green
Corsair Carbide 300R case
As far as I can tell everything is built in fine. I already tried to take out one of the two RAM modules but still nothing. Unplugged the Reset SW on the front panel. The PC always starts up, all four fans (three case and the CPU one) start spinning and after five to ten seconds the PC restarts. The fans stop spinning and directly start to spin again. Also I don't hear any beeps.
Hope you guys may have some input on what I can try next.
Sounds like a PSU problem. Do you have another PSU to test it with?
The other thing to try is to breadboard it; take everything out of the case and attempt to boot with just the PSU, mobo, CPU, CPU fan, and one stick of ram plugged into the board. If this works you may have a standoff problem or dead peripheral.
Remove the GPU also, i5 3570 with that board works with integrated graphics. If you have tried with single stick of RAM try not to put any and see if it beeps if no RAM on board, if it doesnt beep problem might be PSU or motherboard.
And confirm the RAM modules you bought with the officially supported by taht mobo of gigabyte they have a PDF for that board and the RAMs they testes it with. I have the same motehrboard... and at the time I only selected a pair of RAM which was officially tested by them.
Tried to run without any RAM - which is supported by the way - still to no avail. Got no backup PSU so I decided to just turn it into customer support where I bought the components. They did a quick check to see if everything is plugged in the right way and now they completely check every part. So no new PC for the next few days for me. My guess is that the mobo was dead from the factory. I'll keep you informed when I get some news. Thanks for the input anyway