Also the contacts of your card might not be making proper contact with it's receiver - try this, with the phone powered off - insert your card and press again to (un-insert) take card out, then do the same process again - this will help make sure the contacts of the card and it's receiver are touching each other - do this like a half a dozen times.
Next boot (turn on your phone) with the card in and see if it recognizes the card on boot - if not with the phone still powered on take your card out again and re-insert it - sometimes the card contacts and/or the card receiver contacts have a slight coating/sheen on it, making it difficult to get a good contact.
Also it seems that "all" 64gb cards have a small raised square on the bottom of the card probably because 64gb takes more physical space than 32gb and smaller don't have for the extra electronics of the 64gb - turn the card over with the contacts facing up and you will see what I am talking about when you compare a 64gb card to a smaller capacity card - this is a problem with some card receiver, as it basically lifts the contacts of the card from the card receiver because of the extra square - to help overcome that, with the card out press the silver sleeve portion of the card receiver and flatten it somewhat (not to much as you could damage it by press too hard) to make sure it has enough tension over the contacts of the card when re-inserted into the card receiver.
Whew! hope I didn't confuse you - easier to show than explain. That was the problem I had.