Ok, this is probably a goes-without-saying sort of thing, but I’m going to say it anyway because I’ve had these issues and felt really silly when I figured it out. First, make sure the job isn’t set to 1000/1 (or whatever the automatic engrave settings are when you just click it but don’t input anything). Second, make sure there isn’t some silly artifact in your design that is getting “engraved” – when this was my problem, it was a very, very pale, very thin, very long line that essentially wasn’t resulting in a visible engrave. The laser was only doing what I told it… I just didn’t know what I had told it and I kept ending the job when I saw it wasn’t “doing anything”. Only to finally realize it was. Third, clean off the tube as best you can. It’s hard to see very-low powered glow, and a dirty tube can totally obscure it.
None of those are probably your issue, because I’m silly. But someone will be along momentarily with solutions beyond “I’m silly and I need to clean my glowforge”.