Hi John
It sounds like the thermal switch on the radiator may have gone and jammed in the ON position
try to locate the switch it will look like a large brass nut with a plug and some wires comming from it, you can normally trace the wires back to the fan its self
if you locate the switch ( obviously with the engine NOT RUNNING ) just pull the plug off, if the fan stops you will probably hsave to purchase a new switch ( or if budget is tight see your local breakers yard ) sorry Auto mechanical recycling centre
Best of Luck
Twiggy, June 2004