There should be a manual release button on the inside of your boot. A small switch that you need a screwdriver to push it across this should open your boot. The problem could just be the switch. My switch broke in my megane and I took it out check the circuit replaced it with a new one, which cost around £25, put the new one in and no problems since. Apparently the buttons are prone to getting water in them so if you open up the switch a good spray of wd40 may do the trick. :d