Its probably your ignition. I had this problem. My mate sorted it by buying a new ignition and replacing the wires at the back. Im not technically minded, but he did in about 5 minutes. Apparently its something to do with the wiring not being strong enough and ends up melting, which then doesnt send power to the steering. Usually your blowers and rear demisters go at the same time. But not always...
Hope this helps!
Marc
February 2008