Honda civic problems!?

When i start my car there is a loud spluttering sound coming from the muffler. Not from the tip of the muffler but from the underneath up near the engine. the car splutters then the engine just comes off. When you rev the car, the needle goes up to about 4 then the engine just dies out. The O-ring in the muffler has been replaced but the sounds and problems continues. HELP PLEASE!!! I have run out of ideas.