How Much Do I Need To Work Out?

I need to lose between 30 and 40 pounds.  I'm at the point where enough is enough and I know I need to lose the weight because I'm tired of being fat.  I've been working out for about 2 weeks, but haven't really lost inches or weight.  I've been really pushing myself by doing 40-50 minutes 5-6 times a week of pretty hard cardio mixed with weight machines.  My question is:  Do I need to be pushing myself that hard in order to lose weight?  Will brisk walking on the treadmill give me results as much as killing myself with running and stairmaster?

try a combo. of both just alternate days, it works really well. you should start seeing results in 4-5 weeks

You didn't say anything about what you eat.  If you changed nothing about that, and were eating enough so that you were neither gaining nor losing weight, then the level of exercise you're doing would probably be enough to lose about a pound per week.  However, if you're new to strength-training (or aren't, but haven't done it for a while), that would be partially offset by gains in muscle mass at the start.

The only way to know is to get your body fat percentage measured at least monthly, and use that to track how your fat and non-fat weights are changing over time.  That's far more important (to your health and to your appearance) over time than your total weight.

Most people need four things for successful, long-term fat loss without catastrophic lean mass loss:  calorie deficit (burn more than you consume), good nutirition (enough protein and not too much fat), strength training (to preserve lean mass), and cardio work (to burn fat).

Successful long-term losers usually get there with mild or moderate calorie deficits, no more than 1000 per day(*), but never dropping below base metabolic rate (BMR), and eating at or a bit above maintenance level a day or two per week to try to trick the body into not adapting by lowering BMR.

(*) Edit: footnote added:  that's no more than 1000 calories deficit, not 1000 calories per day total.  For example, if total energy expenditure per day is 3000 calories, don't eat less than 3000-1000 = 2000 calories per day.

For nutrition, use the tools on this site to analyze your diet.  A decent place to start is aiming for 55% of your calories from carbs, 25% from protein, and 20% from fats ("good fats", not trans- or saturated fats).  That's a moderately high-protein low-fat diet by government standards, but those were designed for less active people in mind, and neither gaining nor losing weight.  Body fat measurement will tell you whether it's enough protein for you (if you're eating enough and doing strength training, but still losing significant muscle mass, more protein is probably needed).  Perhaps paradoxically, you need to eat "enough" fat for health and to preserve lean mass.  20% of calories from fat isn't rock bottom for this, but should work fine.

Strengh-training is essential to avoid losing lean mass during calorie deficit.  If you were doing it before, keep doing what you were doing.  If you're new to it, two good whole-body strength workouts per week, on non-consecutive days (say, Monday and Thursday) should be enough, under an hour each.

Cardio is important for losing fat.  The harder it feels to you, and the longer and more often you do it, the more calories you're burning.  However, if you feel you're "killing yourself", you won't keep at it, so that's no good.  Many people have lost 100 pounds (or more) over time just by walking.  The lower the intensity (the easier it feels), the longer you need to do it to burn the same number of calories.

If you do everything right (diet and strength-training and cardio), you probably can't lose more than about 1% of your body weight per week without losing too much lean mass.  You may (or may not) be exceptional, but regular body fat measurement will tell you whether you are.  Successful long-term fat losers usually lose less than that per week, and in general the slower the loss the more successful they are over time.

Most people who lose weight don't even do half of it right, and end up fatter than they started two years later.  Believe it or not, that your scale hasn't budged so far is a good sign in a way:  it means you've so far avoided many of the worst mistakes!

Get your body fat percentage measured regularly.  Without that feedback, you're flying blind; but with it, all things are possible.