I find a lot of people who claim to have "tried" diet an exercise haven't effectively done either. "Exercise" does not mean sitting on a recumbant bike for 30 minutes while reading a magazine a few times a week. Sure, it's better than nothing, but it's not going to burn significant calories or increase your basal metabolic rate much. Likewise, "diet" does not mean switching to the "low fat" or "diet" versions of the foods you usually eat.
Effective exercise involves BOTH cardio and strength training. Cardio 5x a week, strength 3x. Unless you have a diagnosed health condition other than weight, it should not be moderate- It should be vigorous. Cardio can be pretty much anything, but it should involve periods above 80% max heart rate. Endurance exercise (1hr+ exertion) at a lower heart rate should be mixed in as well. Proper strength training involves doing sets of major exercises (deadlifts, squats, bench press, rows) until or near failure. Things like dumbell curls and kettlebell swings are fine supplements, but you won't see much in the way of gains from doing endless reps of curls on a 5lb dumbell.
Effective diet involves eating whole unprocessed foods with a lot of micronutrients. Don't drink your calories (most caloric drinks get that way through sugar). While the exact components of an ideal diet are a matter of debate, it's pretty clear than anything that comes in a box or can or sealed bag is a lot less likely to be healthy.
If you do the above, you will burn significant calories from the cardio and significantly increase your basal metabolic rate by adding muscle. Your total calories will likely decrease without any conscious reduction efforts because fresh fruits and veggies will fill you up a lot faster than a bag of Doritos. None of this is rocket science, but sadly is ignored by most people looking to loose weight. Mostly because it involves a lot of hard work (it will take a year of consistent training for your strength efforts to be visible), and because there is no gimmicky product to sell. All you need is the produce aisle, a good barbell set/bench/power rack, and a pair of running shoes.