[Gameplay] Xerath's Q Not Firing

I played Xerath for the first time a few days back because someone suggested him to me and he was on his free week. All was going fine at the start of the game, I was doing great and he played normally. However at one point toward the middle when pressing Q, it would make the noise for being out of mana or on cooldown, (that little clicky sound), when I had 700 mana and it was ready for use. Even clicking on the ability would do the same thing, and showed no range caster when hovered over.

Now, I don't know exactly what did this as I wasn't expecting it, but it was **around the time I leveled it up to rank 3 and bought starting boots. Since I know his Q slows him, maybe the boots messed up his Q? **

I don't know what's going on, but toward the end it caused me a lot of deaths because I would sit there spamming Q and trying to make it work, when it wouldn't.