my 2010 mondeo has been faultless so far and one of the most reliable i ever had. still with original battery started first time after15 days airport parking. still with original front break pads. until today .when i got in switch on ( key less start )  ,i started adjusting the electric mirror as my wife drove the car earlier. in the same time pushed the starting button, and every thing switched off with continuous clinking noise from the main fuse. and become unresponsive to any commands , disconnected the + battery terminal and reconnect start again and looked itself later unlooked. so far  i discpnnected the negative lead from the battery and left overnight.

any advise much appreciated

Sounds like the battery is flat/dead, especially if it is the original. Probably best to get it tested or try charging it if you can, but I suspect you will need a new one.

As per @Frembrit's advice I'd get the battery checked 1st as a dead battery would typically present the kind of symptoms you've described.  As a bonus if it does turn out to be that it's an easy fix.

I would think that the "clicking" noise you mention is from the starter motor and not the fuse. (From what used to be called the Bendix Spring".)  Had to change my 5 year old battery today as the "stop-start" stopped! Due to age, (Mine , not the battery's! ) I took the car to Halfords and had a new battery fitted as it is a pig to change. All now seems well. Before I was convinced that it was indeed battery problems I checked "Messages" in the computer and it also read "Low Voltage".