Technology problems

I've been here before with technology problems but at this stage in my training I really could do without it.  In Copenhagen 2 years ago I lost my computer sensor 2 miles into the bike ride and had to go "on feel" for 110 miles.  Now my computer won't link to my cadence sensor which tells me the number of revolutions per minute my pedals are turning at.  This is important as on the hilly (7,500 ft of climbing) course in Lanzarote I will be focused on heart rate and cadence to monitor the effort I am exerting.  Get this wrong and the marathon at the end could be hell or even worse, I may not make it as I've used up all my reserves!
The computer is also not downloading data to my laptop which makes it difficult to fully analyse the data from my recent long training sessions.
However my swim computer tonight gave me encouraging information showing that I am swimming more efficiently and faster.  It will be very different swimming in the sea with a wet suit but at least I am a more confident swimmer than I was 2 years ago.  Technology plays a large part in analysing your training and in keeping you at the right pace when training.  You've just got to hope it works on the day and if it doesn't, have a plan "B"!