are there any girls in the world that like shy guys?

[Little lunch]

So if heterosexual can become an asexual at will, can an asexual become a heterosexual at will?
What terminology do we use for a person who is born without a sex drive?

I don't know the terminology for that, but asexuality certainly isn't the best one for it, since it can also describe normally heterosexual types who can turn asexual on a whim.

Can an asexual become a heterosexual at will? I have no idea, that is a good question. Personally, I don't know much about the subject of natural asexuality, if there even is such a thing, so I couldn't really answer that. 

You do realize, though, that the two are not correlated. So why are you bringing it up?

Because it was always my understanding that asexual means no sex drive.
The most common form of sex drive being turned off that I have heard of has been as a symptom of depression or stress.