Hi, there is simply no way for us to diagnose this, I'm sorry. My first thought was bloat (because you said his belly is hard), which is very quickly deadly. Please get him to a vet asap. :(
Jenn & TJ
Or this is a Blockage.....Either Bloat or blockage is fatal without immediate Medical treatment....You have an Emergency on your hands......Call your Vet Now before they close.....More than likely, your dog will NOT make it until tomorrow......Make the call! Good luck, Karla
Absolutely agree and hope you have contacted your Vet by now.