My 1998 525td will not start. Was running perfectly until one evening when I came out of work, turned the key in ignition and nothing happened. Battery and starting motor are fine but I am told that I may have a problem with the chip in my key. Breakdown brought me home, tried spare key and car started. Unfortunately the battery in the spare key was flat and would not operate central locking so used dud key to lock and then discovered that the spare did not work!!? Any advice please would be greatly appreciated.