Im afraid my problem is slightly different to yours. I bought everything from e-buyer then built it myself. except the mobo which didnt work so I got a replacement for that at pc world. also I had variouse other components which I reused from my old computer, hard drives the case and the network card. Turns out that was my problem right there. The network card, it must have been shorting out, It seemd odd because I notised it only happend when I was online, but it stopped happening when my isp went down. So I didnt think that could possibly be a hardware issue. It may have been the software actually. Either way. I fixd it by changing the network card.
Oh yeah, also, my fan does seem to be regulating the temprature, keeping it at 40oC. Seems a bit high to me but there hasnt been any problems related to it. touch wood.