Why did Kakashi from naruto start using sharingan with one eye closed?

Maybe because he needed to focus. The sharingan eye can see much more than his regular eye. It would be like trying to watch and remember, what is on 2 different TVs using only one eye each. You can't really.

Edit: but in Episode 27 of Naruto Shippuuden, kakashi had his right eye closed and his left eye open when he had to activate the Mangekyō Sharingan. That was when his Mangekyo appeared. That is why I assumed that when he had to focus on using the Sharingan, or at least the more advanced techniques, he would close his other eye.

and in episode 30 when Deidara had exploded, Kakashi was sitting there with his hand over his left eye and as the fire got closer, he closed his right eye and opened his sharingan eye, so that the Mangekyou technique would take the explosion. I keep getting mixed up on which eye, right or left.

It is probably just some mistake by the artist. Otherwise it could be because his other eye gets tired or something