It's locked up and won't come back so move ahead with the shutdown. Then figure it out from there.

There are a lot of reasons for this to happen but the story isn't enough for me to hazard a guess.
You could tell more but I can't tell if this is a desktop you made or something else. If a desktop, remove the case cover to give max cooling which is a common cause. It's debatable if we call that a hardware issue since many never clean the insides and this does happen exactly as described.