There is no harm of contacting with professors, if you do it right way. Some professors explicitly forbids to write to them about admission. It's better not to do that. Otherwise, you should contact the professors from your field of interests. I suggest not to ask them to help you admit; rather ask them if they would take new students next year so that you would apply(of course after explaining your interests which must match with theirs). Moreover, people say that communication should start well before admission process starts so that professors can understand that you are genuinely interested. Some professors may reply you while some may not. Dont worry, they will consider your application, if they are willing to take new students. Some of the professors I contacted did not respond instantly, but they wrote to me later asking if I am still interested.