Are you using a laptop or something? The # key should work fine unless you are on a special keyboard like a laptop one. If so, you may need to use a certain keystroke or unlock a setting or maybe just hold the FN key while you press it.
As for being unable to melee attack, do you mean you will not even swing at all, or do you mean you can swing, but that you get "invulnerable" messages about your target?
There are a few things that can look confusing when playing on a GM character. Try playing on a normal character on a non-GM account and see if attack works ok then. If so, then your main character probably has a weapon equiped that is too high level requirement to use, or maybe they have #hideme on or something.
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