Before doing this, recheck the description. Did it describe the issue you have (ie doesn't work at all) or was it listed for parts or repair? eBay may not allow refund if the problem you describe is already mentioned in the description. Also eBay is known to not allow refund on part or repair listing if it simply listed as doesn't work and you expected something that wasn't mentioned or pictured.
If you are sure you have a problem, go to My eBay on top of the page and look for Purchase History in the drop down menu. From there, scroll down till you see the item you have problem, look for "More Actions" drop down menu next to the item and select "Return this Item". It should load a return item page with another drop down menu and text box. Select from drop down menu "Doesn't match description or photo" if it's wrong item (ie wrong color, missing part) or "Doesn't work or defective" if it doesn't work as described. Briefly type in the issue in the text box, mention how seller is not responding, and then click request return button on bottom.
