startproblem?

Hi, my citroen C5 HDI does not start when it starts freezing. But when frost is over, there is no problem, even if the battery is almost flat from trying before. When starting problems occur, there is the warning 'disturbance anti-theft device'. But when i keep on trying with cables, the engine finally starts after a couple of times (after it is getting a bit hotter from turning thanks to the startengine). Maybe the injection pump runs empty because of the frost? Can the 'anti-theft device' been switched in the computer? Maybe that helps?