We have a new shower stall (less than 6 mo old), it's not a tub and shower. We've been away 3 weeks and returned to find the sink in bathroom working but not the shower. I pull out the top valve (and the water is to go on). It doesn't and I don't even hear water. I went downstairs to make sure the water is on (my sons have been watching the house). Water valve in bsmt is on/open.
It's a Moen.

Do I understand correctly that you pulled out the handle and turned it left and right for hot and cold but no water comes out the shower head?

What are the outdoor temps in your area, and is your shower valve or supply piping run in or near an exterior wall? I guess what Im asking: is there a chance the water supply has frozen? If no, take the shower head off and see if you get water with it removed. If no, come back and we will take the next step.

You say you pull out the "top" valve. This makes me think you have more than one valve control? One valve controls volume, and one controls temp? Please clarify.

Does it look anything like the pic?