I can't auto-attack anything.
 

I can't attack anything. I can cast spells, and I can shoot arrows, but I can't auto-attack anything.

I've tried zoning out multiple times , and restarting my client, and nothing works.

Try resetting your autoattack key?

I get the message "Auto attack is on." when I hit my hotkey, or when I click on it in my little combat page, but I don't attack.

Tracking can mess with auto attack. Make sure you're not binding a combat hotkey like kick to track my chance.

I did this once for a while forgetting I had steins equipped.

Hotkeys have been the same since level 1, and, no, none of my kick/taunt hotkeys overlap.

Anyways, I apparently found the problem. Earlier, I died in Lfay to a random brownie scout, and I didn't exactly know where I died, so I made a /target Apprentice's hotkey to find my corpse, and it was bound to W/S which are also my movement keys. I moved that hotkey off my hotbar, and, apparently, that was causing some weird conflict which didn't allow me to attack anything.