s60ts wont start

[scoots]

Hello, Iv got a s60ts 51 plate 121k miles, only problem iv got is recently it wont start and a clicking sound comes from the engine. My battery is full charged. It starts sometimes but other times I have to use the jump leads to start it then it starts straight away. There is nothing wrong with the battery. I think its the starter motor. Can anyone help and tell me how to go about geting it fixed without going to volvo cos they want