tube amp/cab help

I just got a cab for my Marshall head, and everything worked fine and sounded great, but when I tried it out again a few hours later, the speakers were humming, and then all of a sudden just stopped working all together. I don't think the power from the amp is getting to the speakers. (both are set at 4ohms, and the amp seems to power up fine) I noticed that the speaker input was slighty loose, but after tightening it, there was still no sound coming through. Could this be a problem with the amps fuse? I dont really know much about tube amps, so any help will be appreciated. Thanks.

The only thing that I can think of would be if your amp was not set to 4ohms.
Either this, or perhaps, you have lost a valve in your poweramp section.
Turn your amp on, and leave it on standby...then take a look at your power tubes and make sure all of them light up to the same degree, if one is not lit...that is your problem...other than that I am not sure what it could be.