boxer dog not eating

Question
my boxer refuses to eat anything and gives black stools.he also had fever 2 days ago.what might be the cause.

Answer
Fever is not the cause for black stools-- Fever is the symptom of infection.

He has an infection that is causing him to loose his appetite and to produce black stools.

This would indict a gastric infection- something he ate or poison.

Get him to the vet ASAP. Do not wait.