problems with the car turning over

Afew weeks ago the car became very juttery. When I was stopped at traffic lights the car would be shaking. This disappeared for a week then yesterday I tried to start the car but wont start. It will turn over and all lights come on the dash. It sometimes does start, you rev it really hard then will just stop. I was wondering if you know what it is and how much for the parts.

Here's hoping you know.

Thanks

Claire