What kind of snake has a grey body yellow belly and a tan ring around its neck?

The snake you are describing is likely the Eastern Hognose Snake (Heterodon platirhinos). These snakes typically have a gray or brown body, a yellow or cream-colored belly, and often exhibit a distinctive pattern that can include a lighter ring around their neck. They are known for their unique hissing and defensive behaviors, as well as their ability to play dead when threatened.