dual-channel memory

I read this sticky thread and now i am wondering how to properly choose a ram. To be honest, i thought memory was the easiest, no-brain part to upgrade. "Just pick the correct DDR, put it in the motherboard and done!" basically, but that doesn't seem to be the case. It seems the correct brand...

Please help me to criticize, Is My another RAM is defective? Cases: No Operating System Single-Channel RAM: Both working up to bios Dual-Channel RAM: got stuck on the screen before the logo (black screen with white dash 'not blinking') With Operating System Single-Channel RAM: the one that...