It could be a multitude of things.
When you are carrying out normal surfing are you having problems? You say you have installed the up to date Java - is it enabled in your browser - tools - internet options - advanced - enable Java Scripts.
Did you check that you have the latest version of Flash Player? If you have you could try uninstalling it, together with Active X, Adobe Flash Player Plug ins and (if you have it Adobe DLM) and then reinstalling - there may be corrupted settings.
Did you try a system restore to before the 20th when the troubles started. It may be as a result of an update.
Are you using Internet Explorer? Have you tried another browser such as Firefox? There are a lot of complaints about the Ebay site just as you mentioned.