Wont Start!

I have a 2001 xsara picasso, everything worked well and then the battery went in October so a new battery was fitted. It worked fine for a while then it started to play up where the dash lights went then returned, it started to struggle to start as it just clicked but would start with a jump leads. The battery was sent back for testing and was informed that it was working correctly. A second hand alternator was fitted and the car worked fine for about 6 weeks but then that alternator failed so a brand new alternator was fitted and the car worked for 1 week! All wiring has been tested and is working fine. A different battery has been fitted and the car was left standing for a week and started every time we tried (ive 2 young children so didnt want to risk breaking down yet again!). So I decided to start using it properly and it has worked for 24 hours and failed again. The car was used for three short trips yesterday and was fine then tried to use it after an hour and it just clicked. It wouldnt jump start down the hill but did start after a couple of attemps on the jump leads. Has anyone please got any ideas? Could it be the starter motor? Could it be shortening out somewhere? Could the battery not be connecting properly? All looks fine but me and my dad are running out of ideas!! Thanks in advance for your help.