Possible electrics issue?

Hi, I'm new to this forum and was wondering if anyone here could shed some light on a problem I've been having with my 2005 Fiesta.

Ever since I bought it its had a problem starting first time. Sometimes it will go a week or so with no problem other time it can take up to 10 tries to get the engine started. Sometimes the engine turns over then dies, other times it 'coughs' then dies, and sometimes there is no sound or response to turning the key at all. I have reason to believe its an electrical problem because often when this happens, the central locking makes a sound, and the dials flash up in odd ways on the dashboard.

When the car eventually starts the dials seem to take a good few seconds to respond. For example the engine will be running but there will be no lights on the dashboard, and the rev counter will stay at 0 for a few seconds while the car is idling then move to its usual idling level. 

Another couple of things that give me reason to believe there is an electrical problem is that the central locking works very occasionally, and the radio also worked occasionally at first and now doest work at all.

It was taken to a garage about 6 months ago and they couldn't diagnose the problem as they said the car started fine each time and they needed it not to start to diagnose the issue.

Any help would be greatly appreciated! Thanks