rplink3r

I need a simple 9V isolated supply for my multimeter. I have many coils, from ATX power suppys lying around in my junk staff, but i dont know how to use them. I tryed with ne555 and a power fet,on freq 150kHz,but the fet got too hot, and i had to shut all down :-\.I tryed many things, on the primary, secondary,the result was always the same. PLZ HELP?!