Try deleting your Yahoo! cookies and sign in again.
To delete your Yahoo! cookies:
- Make sure your browser is closed.
- Go to your Start window and select "Search" or "Find files or Folders."
- Type "Cookies" in the "Named" window in the Name & Location tab.
- Double-click the yellow folder that says "Cookies" to open it.
- You can either select all the cookies and press Delete, or you can look for the (yourname)@yahoo cookie and delete that.
If you continue to have problems logging into our services, visit our Sign-In and Registration Help area.