I have tried rebooting a few times to no avail. I'm not sure what I was doing. I think they were working fine when I stopped using my phone for a bit (or at least I hadn't noticed them not working). I then came back to my phone a few minutes later and they had disappeared.
How new is the phone? If it's the soft keys, then it may be a hardware defect. Try talking to the store where you got it, or to Samsung, about a replacement or repair.
Do you mean it's a new phone and the key lighting has gone out, or when you touch the back or left key, or hold the left key for menu, nothing happens.