I have a W reg renault clio, wont start, replaced key?

I have a W reg clio which wouldnt start and had the red flashing light on the dash, was told that i needed a new key so paid £120 for a new one and the car still wont work. I was just wondering do these things that go under the ashtray work and should i try my luck???? Help.... Ive had no car for 5 weeks and its gettin frustrating!!!