Nutrition is a big part of either losing weight or gaining weight. Only about 35% of total caloric expenditure comes from your physical activity. Almost half stems from your basal metabolic rate (the energy your body consumes from normal physiologic functioning) and a small percentage (10-15%) from the so-called Thermogenic effect of differing macronutrients.
Normally, for most people, you will start to 'see' your abs when you come down to about 9-10% body fat.
Each gram of carbs represents about 4 Kcals, proteins about 4 Kcals, and Fat about 9 Kcals. Because there are 454 grams in 1 pound, then mathematically speaking, there is 4086 kcals in 1 pound of fat (i.e. 454 g x 9 Kcal/g).
In the body, fat is stored in the form of triglycerides in adipose tissue. However, 1 molecule of adipose tissue is not 100% fat. Some 5-10% is water (which contains zero calories). This is just an estimation, but currently it is believed that adipose tissue consists of about 84-87% fat, hence the infamous "1 lb of fat equals 3500 kcals" statement you often hear of (454 g x 9 Kcal/g x 86%).
If you try to lose more than 1-2% of your total body weight per week, you will start to lose muscle mass as part of the 'weight loss'. This is why you often hear that safe weight loss involves no more than 1 to 2 lbs per week.
I prefer to lose weight slowly (1 lb/week) and I am always more concerned with losing body fat than 'weight'. So this generally means you must create a caloric deficit of about 3500 kcals per week.
This deficit can either come in the form of caloric restriction, energy expenditure, or, preferably a combination of both.
While resistance training is great for building muscle mass (or at least minimizing muscle mass loss during caloric restriction) it does not burn a substantial amount of kcals to achieve your caloric goals. Exercises utilizing large muscle groups, rythmic or dynamic movement for prolonged periods burn more kcals (i.e. cardiovascular exercise) for this purpose.
Generally, the interaction of intensity, duration and frequency determines caloric expenditure from the activity you choose.
There is a genetic influence. However, I would first see about my training regimen and nutrition plan before reverting to other measures. Before you can determine what to do, you need to analyze what you've done. This means knowing what your current training is expending in terms of kcals, and knowing how many kcals you are ingesting daily. Without this information, it will be hard to determine what you should be doing next.
In terms of cardio, I never run. After a thorough warm-up, I will set the treadmill to the highest incline (10-15% grade) and walk at 3.5-4.0 mph.
Hope this helps.