All the lights on my Citreon C3 Pluriel dashboard have lit up!?

Most lights have lit up, the ABS, airbag, petrol gauge is showing nil, handbrake, and when the radio or CD is on it constantly beeps at me. It also doesnt show the speedometer either now.
This happened last year and a loacl mechanic told us how to fix it, some bizarre sequence of events like
'open door, open window, shut door, turn key in ignition, turn off, unplug battery...' When we did it, it went all back to normal...but i cant remember it and need to fix it as soon as i can.


does anybody know this sequence that i mean?