Citroen C3: Citroen C3 1.4HDi 2002, wont start. Turn key and…

About June last year I had stoped the car but when I came to restart it I had the same symptoms as described, all indications normal untill when I turned the key the engine didn't turn over. At that time I checked all the fuses, which were fine, and I also tried rocking the car while in gear in case the starter was jammed but this made no difference. I was close to a garage and they tried to jump start but this had no effect and they said it appeared to be an immobiliser problem. The battery was disconnected for a couple of minutes but this had no effect. We then tried to bump start and this worked and I was able to drive the car and everything worked. The car was fine for a number of days but then the problem happened again. Again i got it bump started and all was fine. I then noticed that having just starting (and with the engine running-not normaly a good idea I know) if I then turned the key, as if to start, the starter still did not engage but after diving a couple more miles and doing it again the starter did come to life. All this repeated itself a couple more times over a month or so but then the problem went away without needing further rectification. It may be not connected but I also had occasions where after starting the car normaly the power steering was very heavey as if not fully powered. This problem didn't occur at the same time and was more frequent but went away at the same time. Over the last month the car has struggled to start, sometimes it didn't, after a really cold niight. Saturday morning I had to jump start the car and on this occasion the problem with the steering reoccured. Later that day I replaced the battery, the replacement was a slightly more heavy duty than the original. The car was fine the remainder of the day and Sunday. Monday morning, after not a very cold night, it did not start. Tried a jump start no luck, tried rocking the car, no luck. A look around the engine showed nothing obvious. There is a control module located along side the battery with three plugs on, I disconnected these but they apeared clean and all the pins were in good condition. The wires going into the plugs are loosley bound but moving them around while trying to start the car had no effect. I focused on this because it was moved (not disconnected) when the battery was changed. Later I got a push and the car started (again the same thing when turning the key with engine running, same result). Drove around and all seemed fine, steering was heavy. Came to the car this morning and again dash lit up but the engine did not turn over.