I'll seriously rethink doing my PhD under the supervision of an academic who failed to reply my email after two initial contacts. Things do, and can, happen: there could be problems with her/his email; s/he may have become suddenly hospitalized; s/he may be away (e.g. field-working in some remote locations of the world where there is limited or no access to email facilities--automated response should have been set up in this case); s/he may no longer be in that university. Short of these, or any similar reasons, if s/he has simply ignored/failed to reply your emails, it could be a sign that s/he would treat you in much the same way when you start your PhD with her/him. Your worst nightmare would be to send materials to your supervisor to read and provide feedbacks but fail to get any responses from her/him, even after several reminders. As HazyJane remarked, try and contact the departmental secretary or administrator and find out whether or not this academic has been around. Best of luck.