Hi I had a Dell Dimension e521. Recently my video card(it was an upgraded card, not the original, had a small fan in it)overheated. I replaced it with the original video card, which works fine. The overheating seems to have been caused by the heat sink and system fan(they are attached) being clogged with a large amount of dust. I tried compressed air and even a small brush, but could not get to it. I resorted to removing the heat sink from the processor, removing the dust, cleaning the old thermal paste off and reapplying new thermal paste. The computer is now running normally, except that the fan is stuck on high speed. I downloaded speedfan, and system is running cool. I have tried updating the bios, this did not fix it. Speedfan does not recognize my fan settings and i cannot modify them using it. I opened up the case and found the fan connector on the motherboard, unplugged it and replugged it. no change. Computer is working, and not overheating, but this is really annoying? I am considering replacing the fan, any other suggestions?