had same problem with mine today....stick it in gear, turn the wheels to free the starter if its stuck.
disconnect battery, get under car, and take the spade terminal off the agitator on the starter (ie the wire that's not bolted on)
clean the now visible spade with emery paper to remove oxidisation (rust, corrosion, the grey/blue stuff) until its shiny and new
stick the spade back on, smear some vaseline on the connection, recoonect the battery and it's job done
who'd have thought a thin piece of metal a foot from the road would get corroded after months of driving through floods and snow???
hope this helps someone like me pulling heair out, cursing and imagining a £££ garage bill.
PS - sell useless french car and buy Volvo to prevent this problem in future =D
Wilse
February 2013