Could it be the imobilliser?

Hi I have a Clio and over the last month it has been clonking out for no reason..firstly I had the battery tested and the battery was fine checked to see if there was a petrol leak and there was no sign of a petrol leak...a day or two later my car started but over the last couple of weeks it has been playing up so I fitted a new crank shaft and the car would still not start so I banged the starter motor a few times and tried it again and the car started so I then brought a new starter motors and fitted it and the car was running fun up until today i went to work locked my car up and when I went back to my car I unlocked it and it would not start it was just turning over...
When I put my key in the ignition the light for the immobiliser flashes so I tried to re-sync the key with the car after trying this the car would still not start but now the imobilliser light id staying on when turning the key in the ignition and not going off... Could this be a problem with my key fob or something else??