upgrading single ram block on defect motherboard.

Hello win7 community, I am hoping to get some good advice as I find my knowledge has come a bit short, after a problematic troubleshoot.

The problem:
I have been having a lot of different crashes on my computer for the last while, but have not really been looking too much into it. So I finally decided to look into it, and figured it looked to be RAM errors. So I ran a memtest86 and just as I thought, it gave me a bunch of errors. I went on troubleshooting, and found that both my ram blocks was working fine, in the first slot, and in the second slot as well. That confused me quite a bit, but I figured it might not be the problem after all. So I looked up CPU-ID, and found that the my memory only showed the second ram slot. So I went back to testing, now with the result that I am unable to boot my computer while having only ram in the first slot, but it works perfectly in the second slot.
At the moment I am running with only a single ram block, and a total of 2gb ram. I would like to have a more, as it feels a bit limiting.

My question is if I can upgrade my single slot to 4 or maybe 8gb ram, instead of buying a completely new computer, as a defect motherboard would usually result in, or will running with only one ram slot make to many problems?

I have a few specs if you need them
Motherboard: ASRock H55M-LE
RAM is 2gb Kingston ValueRAM DDR3 PC3-10700 (667MHz)
my OS is windows 7 home premium 64bit.

If there is any needed information I have not provided please tell me. :)

Thanks for the reply. I think I will get a 4gb Ram block then. It is horrible to be running with only 2gb. And there is a huge price difference between a new pc and a Ram block.