Hi, I'm a new member please help!!!

I have a Mondeo 2004 TDCi. It has started 1st time every time since I've had it approx 6 months... including 4 times yesterday. This morning and agian this afternoon however it is failing to start. The Imobiliser light comes on for approx 3 seconds before going out when I turn the ignition on. When I try to start the engine nothing happens at all, no noise from the starter motor or anything. I can hear some faint buzzing noises when the ignition is turned on/off. When I parked up last night I switched the engine off whilst I was slowing to a stop, only 10 feet or so before halting.(paniced as all my Sisters and Brothers cars were at the house and my Dad is unwell, thought something may have happened). Thanks for any help.