Citroen xsara 1.4lxi 2001 struggles to start?

Sometimes my Citroen Xsara 1.4lx 2001 struggles to start. It will start and then cut out, on turning the key again there is a loss of power and a electrical noise ( maybe the ecu ). I occasionally have to reset the time and date on the dash after the car eventually starts because it starts flashing for re-setting.