Hi!

I've got a Fiat Marea Weekend 2001 1.6. I have experienced some technical problems lately with the heater, and now it is not operational at all. None of the instruments work, and neither the temperature button. All the other buttons on the instrument panel work properly, but the heater seems to be dead.. What can I do? Is there an electric issue?

First thing to do is check all the fuses that protect the equipment that has stopped working. If they are all ok then I would take the dash apart and make sure one of the multi-pin connectors hasn't dropped out. They all have catches that hold them in but if someone has been in there and not pushed them home fully the catches might not have engaged.
If they are all in place then it is down to old fashioned fault finding, if you are not confident with multimeters and circuit diagrams you may have to go to an auto electrician.
Good luck