I've contacted professors there successfully and will be applying. You may have just hit a busy time frame--this is my second year applying, and I learned from last time that contacting professors before the new semester begins seems to glean more thorough and prompt responses. Similar to the suggestions above, I would contact the admin folks and see if they know who is accepting mentees. To my knowledge, all PhD programs will want you to identify a POI. At least the ones I've looked at.