Why the heck would they lock the button from inside the box?
I really can't fathom the way some of this stuff is shipped from these places - you buy a machine, in good faith that it will work out of the box, in the end its a construction project or rewire job. Yes it's a budget item but it should still perform basic functions surely?
The internet is loaded with stories on all of these models - 3040, 6040, 6090, mostly all in a negative light.
I hope the OP gets it going and it seems wollyacresfarms has a decent bit of knowledge there.