If you are not getting a response, how do you know the seller has not shipped the item?
Not all sellers mark the item as shipped with the little envelope icon. Moreover, a seller has 7 days to put it the item in the mail, although very few ever take that long. If you have contacted the seller but have not had a reply, he probably just thinks you're nagging.
If, on the other hand, you wait 4 weeks and still no item, that's different. In that case, contact the seller to inquire, and if you get no satisfaction that way, you may need to open a claim for Item Not Received. You have 45 days from when you paid in which to do this, and that's just over 6 weeks.
The following link will tell you what to do if there is ever a problem, either a no-show item or not as described. There is a link to the Resolution Center if you need it. Have a look, it is the most useful information you can get if you plan to buy very much on ebay:
http://pages.ebay.ca/help/buy/item-not-received.html
If ever you need to file a claim, do so no later than day 43 to be 'safe'. Never close a claim until you have your refund back or your item, because a closed claim can never be reopened.
Most items show up, although the mail seems a teensy bit slower these days, so I'm sure yours will be along very soon.
Hope you like it. 🙂