Good camera for someone wanting to start a business?

I'm in the market to upgrade to a more professional camera. My current camera has taught me about as much as it can and now it's time to move on.
I would like suggestions on what type of camera I should be looking into. I know Canon and Nikon are the most recommended. I've been looking into both brands. I think I might have settled on the Nikon D5100. Reasons for that, I don't feel that I'm ready for the more fancy, high end cameras yet. I don't want to purchase something that is too far past my knowledge and ability to learn quickly. I have minimal knowledge of the manual settings for iso, f-stop, shutter, etc. I study and practice almost daily, but I don't want to be overwhelmed with a camera that is just "too much" for me.
I appreciate your feedback and any suggestions you may have.
Thanks in advance.

Added (1). Say what you will, but I'm not going to jump into a business blind. There's a point where you know you love something, you know you have a lot to learn, you are willing to do just that and then you start putting things into motion to get you where you want to be. I'm not going to lie and pretend I know everything there's to know about this field. I'm spending my days studying. Not just about using a camera, but what it takes to be in business. It always seems that established persons forget that they, too, once had to learn everything about their fields, and their art. Usually, that learning to took time, and most keep learning even well into being a master of their craft. Don't be so quick to judge me. If my honesty sounds idiotic to you, so be it.

Added (2). My camera has taught me HOW to use the manual features, but the quality is not where it should be, or where I want it to be. I'm not satisfied with the limits my camera puts on me. I love to shoot everything from people, whether it be portraits or not, nature; trees, animals in their own settings, pets, anything that catches my attention and inspires me to shoot.

OK look here…

You want to start a photography business, but you don't want a camera that is too much for you?

This is one of the more idiotic things I have heard.

What if I said, "I want to be a professional race car driver. I don't know how to drive, but I was thinking about getting a used Ford?" That is basically what you are saying here.

Tim's answer is quite crude, but quite accurate.

The D5100 is a fine camera, and it is more than capabable of starting a photography business. However, most (except for a handful) of photography business fail because of the person; for any of the following reasons.
- the person does not know how to use their camera (minimal knowledge about manual settings)
- the person does not have a business plan
- the person has no clients.

In a photography business, the camera should be an afterthought. The most important part is that it is a business, a business people rely on to feed themsevles, their family, their car and other obsessions. People pay money to photographers because the clients themselves, know nothing about camera, nor about light, nor anything else. They place their trust into the photographers. If you are unable to deliever on this very basic front, there's little chance your photography business will succeed (unless you run one of those minilabs that takes passport photos).

I'm wondering what you expect to learn from a new camera that your current camera hasn't already taught you. All cameras have controls for ISO, shutter speed, aperture, and (most) focal length. Unless your current camera is a Holga, in which case it didn't teach you anything.

Another way to put it is what do you think will be the benefit of an upgrade? How does your current camera limit your photographic horizons? If you can answer that question, then you will be on your way to deciding what your next camera should be. Do you want to specialize in portraits, family pictures, weddings, fashion, product photography, events, fine art? Which? That will tell you what kind of gear you need.

Nikon D40.It will run you about $500 new. $300 used. My Nikon D40 is my baby and it takes great photos! It's also really good for beginners. This is the camera I use to shoot everything. My pictures always turn out great!

Hope this helps

I'm not even going to discuss the business idea, pointless.

I'd get a used D300, few decent lenses

Most people use an SLR camera. Get one of those.

As far as which one to get; that will be your job to figure out. That's one of the responsibilities for working for yourself. Research.