Vector space basics: scalar times a nonzero vector = zero implies scalar = zero?
An idea for you on the same varation: suppose the scalar $\;a\in\Bbb F\;$ is not zero. It then has an inverse $\;a^{-1}\;$, and:
$$av=0\implies a^{-1}(av)=a^{-1}0\implies 1\cdot v=0\implies v=0$$
The above assume you already know that scalar times the zero vector equals the zero vector...
Hint: There was that axiom that said that $1v=v$, was there not?