ford focus key fob wont unlock doors or boot?

i have a ford focus 1.8 petrol zetec 2001 reg, the key starts the car and used to unlock the boot and doors by remote,i have turned the key in ignition 4 times and can hear the first audio signal,however when i remove the key and try pressing the buttons on the fob there is no second audio signal.the led next to the clock flashes as normal and only stays on when you first start the engine as normal i have tried this many times please help