Is this the question in its entirety? If so, is there context to the question?
I ask this because the question, as you have posed it, is a very bad question. The technically correct answer is "Yes." Providing a rigorous demonstration was beyond the powers of three centuries of very great mathematicians, including Gauss.
http://en.wikipedia.org/wiki/Fundamental_theorem_of_algebra
On the basis of the theorem discussed in the article cited above, you should be able to construct a non-rigorous explanation of the technically correct answer.
Hint: How many real and complex roots do cubic and quartic equations have respectively? What does that imply?