If your cat won't urinate, it could have a blockage in its urinary tract. There might be some crystals that formed and are preventing urine from passing. If you noticed any blood in the urine prior to the cat not being able to urinate, then it is a good chance that that is the problem.
It could be a bladder infection, or, especially if it is a female, it could be a urinary tract infection. In either case, you need to go to the vet, because the cat will most likely need an antibiotic.
It could be a urinary track infection or possibly a problem with a blockage in the cats ureter. The infection you treat with medicine. The ureter blockage requires surgery.
