Kia ceed 1,6 dielsen 2008 (wont start, only sometimes)

Hi every one
I have a kia ceed 1.6 diesel from 2008 and it has problems starting. I can turn the key also says the sound from the key is turned until the engine takes hold. It also just drives with that sound without starting, if I keep going it can start once in a while. I have tried to reset the battery and check the oil and fuses etc. I have also spoken to my neighbor who is a mechanic and he measured with measuring equipment that there was something wrong with the immobilizer, anyone have an idea. I think it can be fixed as it can start a sometimes times.