Try clearing cookies
On Firefox top left on the drop down list clear history.
Internet Explorer 7 go to Tools then Internet Options then Browsing History
To clear cookies from other browsers search on the internet
by putting in the name of the browser for example Clear Cookies on Chrome or whatever browser you are using.
If that does not work restart your computer.
Or try another browser Firefox works well with ebay or Chrome.
You can have more than one browser on your computer