I have a Trane XR80 furnace. I came home last night to a cold house. Went through all of the troubleshooting points but it still blows cold air. Any thoughts?

Did you use a meter to find out why it was not working? You should have 24 volts to gas valve, if you have gas. Get a volt/ohm meter and I can tell you how to know in a few minutes what the problem is and what to do. It is very easy.