My Dog Is Throwing Up A Dark Brown Liquid, He Hasn't Ate Or Drank Anything In The Past 3 Days, Also Has Lost Most Of His Energy. What Could It Be?

The symptoms you describe sound rather serious and I would advise you to take your dog to the vet as soon as possible to get a proper and professional diagnosis of the problem. Any advice given here will only be general and should not be taken as recommended for your situation. The only way you will be able to treat the problem effectively is to seek the advice of an expert.
There are a number of potential reasons that your dog is displaying these symptoms. He may have a flu-like virus which is suppressing his appetite and making him feel sick. In this case your vet may prescribe medication such as intestinal medicine in order to treat the illness and restore your dog to full health.
Alternatively, it is possible that your dog is overdue having their teeth cleaned, which means that they are suffering from a build-up of tartar which would make it uncomfortable to chew. This would explain why they are unwilling or unable to eat any food at the moment, possibly causing them to feel sick as a result.
You can find some general information about illness in dogs at How Stuff Works (animals.howstuffworks.com/pets/medical-treatment-for-dogs-ga) but ultimately the only sure way of understanding what is wrong with your dog is to take them to the vet as soon as you possibly can.

Take your dog to the doctor as soon as possible. This might be happening because of undigested food. Over eating and food poisoning can be the simple reason. Feed a bland diet that consists rice, oatmeal and sweet potato and cook it well. But you should consult the vet immediately. Don't forget to check the following website.
 
www.free-online-veterinarian-advice.com
 
 

I am having the same problem with my dog. I took her to the vet and they told me she got sick from raw hides. I gave her the medicine she was supposed to have. She got a little better over the next week and stopped throwing up and eating again. I threw the raw hides away. Then all the sudden, she started throwing up the brown stuff again. Took her to the vets...again! This time, they took blood, said everything was fine, gave us more pills to stop her from throwing up and sent us on our way, $300 later. She is STILL throwing up. Not eating @ all (not even canned food...and she was a pig...overweight dog). She lost A LOT of weight!!!!! I don't know what else to do with her. Had her to the vets twice and they seem to think this is something that is going to pass.

Take your dog to the vet if its stopped eating, it can die quickly like that. It may have been poisoned.

Three days of vomiting?  Rlall is right...take the dog to the vet!!