I am going to assume we're talking about a student who plans to apply to the PhD program that the faculty is affiliated with, but has not yet been admitted. (You didn't say explicitly, but reading between the lines, that is my assumption.)
If that's the case then the student should not expect a response and should not read anything into the lack of a response from the faculty member. Many faculty do not have time to respond personally to all enquiries from prospective applicants.
Please understand that some faculty receive dozens or hundreds of enquiries from prospective students. For example, my understanding is that many Indian or Chinese students are under the mistaken impression that they should contact faculty, or think it will help their case for admission somehow (not true; but they don't know, or have been given bad advice, so they write). Anyway, as a result, many faculty cannot possibly reply to all such contacts. I've even seen a few faculty post a FAQ on their web page which explains why they cannot respond to such inquiries from prospective PhD students who are interested in applying. In many cases, it is likely that few or none of those who contact the professor will be admitted, so professors may understandable decide that they cannot afford to to spend time responding to such contacts until after admission, in most cases.
To learn more about this, I can recommend some additional reading:
Advice for Prospective Research Students - a FAQ one professor posts, about how to contact professors
Writing to me - Advice from Female Science Professor (a pseudonymous professor/blogger) about how prospective grad students should write to her.
In general, anything from FSP is worth reading. Here are some additional posts of her that are relevant, and that may help to understand the professor's mindset:
If I have misunderstood the status of this student:
If the student has already been admitted into the PhD program where the faculty is affiliated with, but has not yet accepted the offer of admission, the lack of response probably indicates lack of interest or lack of time on the part of the faculty member. In this case, my advice would be to move on. As far as I can tell, though, this response would be a bit unusual: if the student has been admitted, it typically means that at least some quorum of faculty think highly of the student.
Finally, if the student is current enrolled in the faculty's PhD program, the student should go visit the faculty member in person. Faculty have office hours; go use them.