Electrical fault?

My 98 plate Megane Scenic randomly won't start. When it fails, the electrical fault symbol flashes and the engine just ticks over with out firing up. I was away for 3 weeks and the problem started after this. I remember calling the AA out last year for the same problem, but when the guy came it started fine and then didn't trouble me again. This couldn't be a blown fuse as about half the time it does start no problems. Any ideas? Reading other posts I'd say it has something to do with damp, can anyone suggest where I need to focus? Thanks.