My two year old Fox terrier refuses to eat or drink. I took him to the vet yesterday and had xray's and bloodwork done on him to check for a vuirus or blockage in his stomach, but both came back as negative. However, he still refuses to eat or drink. He remains active and energetic. Any ideas, he has not eaten in 3 days?

This sounds bad. Unless there is some cause for an emotional upset, likely he is sick. It may be something that has to get worse before the vet can tell what it is. Not eating shouldn't be a problem for several more days, but the water is a problem. Try flavored waters. Avoid sports drinks or Pedalyte. He already has excessive electrolytes. Ice cubes might help too. Don't give him a laxative. Don't try to tempt him with rich food. Stay in touch with the vet, and maybe even think about a second opinion.