My senior dog won't eat or drink and seems very tired. What's wrong?

Refusing food can be caused by a huge number of things. Urine gets much darker when a patient is dehydrated. So, since Cody is not eating or drinking normally, we would expect his urine to be darker than normal. Dehydration alone can make a dog nauseous and refuse to eat. Dehydration can also make a number of conditions worse. I would recommend having your vet examine Cody ASAP to see if they can figure out what is causing Cody not to eat. They may need to check some blood work to figure that out. Depending on what they find, at the very least, they will be able to give him fluids to correct his dehydration which will make him feel better and maybe give him anti-nausea medication which may allow him to start eating again.
Good luck! I hope that was helpful and that Cody feels better soon. Thanks for using Petco Pet Education Center, formerly Petcoach.