heater not working?

Please help......
Problem: heater has stopped working, a/c light doesn't work either too. Demister light working but not blowing any air out. The heater isn't blowing any air out either. You can imagine it at the moment. I can't see out of the window to drive in this weather.

Any ideas what the problem is?

The problem is on a citroen picasso (51 plate). It was working a few days ago and now just stopped. Had a diagnostic check and engine seems to be coming up "sound". No problems. Fuses have been checked, no lose wiring; just not working.