Bad motherboard? 2 RAM slots bad

hi there, well one day my rig was working fine and dandy then I went on vacation and when I came back it wouldnt boot. It turned on (fans turned on and HDD started up) but the monitor wasnt getting a signal and my mouse/keyboard wasnt lighting up. So first thing i checked was the RAM. I took all but one stick out and it booted up fine. So I then tested the other sticks of memory in the first slot and they all worked too. Which proves that my RAM is good right? Well my motherboard has dual channel so the ram slots look like 1- A and B (blue) and 2- A and B (black). Where the A and B are paired. So at this point I have tested all 4 of my RAM sticks in slot 1-A. Long story short I repeated putting 1 stick of RAM in all four slots and trying to boot. It turns out that 1-A and 2-A arent working. And Ive tried just about every combination of putting 4 sticks in, 2 sticks, switching them up ect. So, right now Im running 2/4 of my RAM sticks in slots 1-B and 2-B which doesnt even let them dual channel. I guess my question is: Does this absolutly mean that my motherboard is bad? Is there anything else I should test? What made these 2 ram slots go bad? How effective is it running right now (ie what does the dual channel actually do)?

Thanks in advance.