I had the same problem and it ended up being the fuse... if you've checked that and it's not it, maybe the bulb behind the cluster?
And the obvious, check the dial for dimness to make sure you didn't hit it and knock into it all the way dim.
When I had my problem before I knew it was the fuse, someone suggested the headlights switch. If the connection is getting bad, it might not touch that part correctly, but still turn on the headlights. This is a bit far out I think, but it was suggested to me.
Anything beyond that is probably an electrical issue. =/