Yup I finally figured it out. Two weeks ago, my motherboard stopped working. So I bought a new one. Now the fan is working properly. So it seems the problem was with the motherboard. I gave the motherboard to a friend of mine who ran some tests. He said the motherboard is missing a chip which should have been there. He showed me a couple working DG35ECs with the said chip in place. I don't know how I lost this chip (or if it was there in the first place).
I dont know if the missing chip caused this issue, but it certainly was related to the motherboard.