1. Whatever begins to exist has a cause.
2. The universe began to exist.
3. Therefore, the universe has a cause. 
One argument offered in support of Premise (2) is the impossibility of an actually infinite number of things. The argument goes like this:
1. An actually infinite number of things cannot exist.
2. A beginningless series of events in time entails an actually infinite number of things.
3. Therefore, a beginningless series of events in time cannot exist. 
However, this often raises the question, "If an actually infinite number of things cannot exist, how can God be infinite as theists claim?"
As William Lane Craig explains, this question is based on a misunderstanding:
"When we speak of the infinity of God, we are not using the word in a mathematical sense to refer to an aggregate of an infinite number of finite parts. God's infinity is, if you will, qualitative, not quantitative. It means that God is metaphysically necessary, morally perfect, omnipotent, omniscient, eternal, etc." 
Courage and Godspeed,
1. To learn more about the Kalam cosmological argument, checkout this outstanding short video.
2. William Lane Craig, Reasonable Faith, 3rd Ed., p. 116.
3. Ibid., p. 119; Emphasis mine.