Citroen C5 computer/electrical problems - desperate for help

We've got a 52 plate c5 2 litre sx hdi estate, and started having problems about 4 years ago with the dashboard/electronics/fan. At the moment the dials are very sporadic in working, they will go off for a few minutes or months. We have no speedo, rev counter, fuel, engine temp, mileage (or trip) or oil temp gauges. The warning lights which are always lit are - passenger airbag disengaged, abs fault, handbrake warning, service light, and the stop light. The indicators work but don't light on the dash. The hazard lights neither work or display. Some time ago the fan failed and there was an electrical burning smell, like an electrical motor. The fan never worked after that. It has just been replaced last month and still doesn't work, and the old fan that came out has been tested and also worked fine. I've been to citroen and they had a look, they are pretty stumped and would basically need a blank cheque to start looking. I'm quite confident to have a look about in the car, if anyone has any suggestions as to what the problem might be or maybe some help for how to get the dashboard off? It's just failed the MOT today (which has cancelled our holiday) so basically means the car is scrapped if we can't get to the back of this. The car drives perfectly, no loss in performance, suspension is fine etc. Also the cd player cannot be used, while the instruments are down, as it makes a very loud beeping noise, almost like an alarm. Don't know if this is connected to the rest of the problems. Again any help is very much appreciated, getting pretty sick of these problems now. Thankyou