What model rover ?? these cars have a pecular trait and that is if the key is left in with ignition on for more than 30 secs then immobilisor comes on and can only be released with the fob by locking and unlocking the car with the fob ,If no parts available then in a box somewhere i have all the computer /transponder ,key ,fob and the key code number as well for a 99 rover 400 which i can post to you .Although in the past i have by-passed the immobilisor by bridging a big transistor collector and emmiter connections same as i have done with a escort and a focus as well ,the dammed renaults you get it started then cut the third wire on the transponder while its running .But this isnt helping you ,use the FOB and make sure the key has a chip in it and it hasnt lost the chip