when you toggle the Melee Attack button is there a notification that it is on - as my berserker doesn't seem to auto-attack half the time; leading me then to use the mouse which seems to alter the setting again... I am probably being very stupid but this is game-breaking at the moment for me as the combat system is too slow otherwise with the huge cool downs of melee abilities....
If I remember, your auto-attack swings are based on the delay on your primary weapon. There is an auto-attack timer in the game to help you see this (Options>User Interface>Game Windows>Show the Autoattack Timing Bar), but I think most berserkers are set on a 4-second delay on their weapons. The idea is to fill the time while your timer is moving with attacks from your bar, and auto-attack on the finish of the timer. So a 4-second weapon delay would be filled with roughly 3 1/2 seconds of hotbar attacks, and the last half- or quarter-second with the timer finish before the timer starts over again. Also helpful is to make sure both your primary and secondary weapons have the same delay; if they don't the movements become ill-timed and choppy. Your weapons can be set on a 6-second delay, which would make them hit harder, but would lessen the amount of swings you do overall (more swings *usually* = more damage). Honestly, though, at this point in the game, auto-attack is usually less than 2% of your parse, behind ascensions and all other skills. Unless they fix it to mean something more again, I wouldn't put much worry into it. Also, if you don't like the slowness of a berserker, try a brawler. They're much, much faster paced.
I don't know about berserkers, but I've noticed that on most classes that cast magic, a lot of the time, if you cast a spell, your auto-attack turns off. The only indication that I know of if your auto-attack is on or not is the Autoattack timing bar Mercychalice mentioned.
Open up your character sheet, go to the options tab, scroll all the way to the bottom, and select "Automatic" for your auto-attack mode.
OK, I messed around with this a little bit. What do the options actually do? I'm not seeing anything different when I change them?
If you're a caster, it should make it so casting spells doesn't turn off the auto-attack. If you're not a caster, then using any combat art should start your auto-attack.
Check that you have a wand, not a symbol, in your ranged slot if you're caster.. Wands do spell ranged auto-attack. Symbols do not.