Elsword USA Open Beta Announced!

This is just a stab in the dark. But try restarting your computer if you are unable to use any skills.
Had a similar problem with maple where I was unable to use certain skills. So maybe there's something in common. If that doesn't resolve it, then ignore me. lol

... And just in case. You just press the key that corresponds to the skill[ASDC] when you have enough MP. Doubt that is your problem though...