Try removing extra hardware to see if you can manage to get it to boot. I.e. only have the essentials plugged in - one stick of RAM and the graphics card. Remove all extra PCI(e), USB, optical and storage devices.
Would your friend be able to help you out some more by borrowing some of his hardware? Perhaps even him letting you test out some of your hardware in his machine? This will let you rule out which components are functioning correctly.