Sorry to say, but you're out of luck at this point.
The deadline to leave feedback and/or open a Paypal dispute is 45 days. It is a good practice to open a dispute around the 40-42 day mark, and close it once the item is received-that way you get a bit longer to get the item.
The seller is most likely not replying to your messages because he/she know that you are no longer able to open a case against them. While this may be morally wrong, is not uncommon.
Take it as a learning experience. Hopefully you get the item soon, and if not... hopefully it wasn't too expensive!