Hey Format,
Don't know if you are worried about cost, but the chipset fan on my old Asus A8N-SLI went out as well. I just called up ASUS support and they sent me a new one for free.
My Gigabyte DS3L will do it anytime I set a bad overclock. IE, FSB too high, not enough volts, bad RAM timing, etc.. Just tweaking that stuff back to a suitable range fixes the problem. I could always tell when the board would reset itself because on POST the machine would shut down and start...
Got mine at futurepowerpc.com
http://www.futurepowerpc.com/scripts/product.asp?PRDCODE=CPIN-RE8400
Free shipping and no tax for us Cali peeps. CPU shipped out right away as well. It was $215.99 when I bought it though. Seems to be $227.99 now, but looks like it is still in stock.