I too experienced your problems last week and fixed them on both my browsers - Google Chrome and Firefox.

If your using Google Chrome, hold down the following keys, Ctrl,Shift ,Delete.The clear history tab will appear.Select all of the 4 following, Browsing History,Download History,Cached Image Files,Cookies & Other Site Data,Press the blue ''Clear Browser ''data button.Exite the screen and try signing in to e bay.

If your using Mozilla Firefox, open up your Firefox panel.Go to Firefox help (? mark symbol bottom right corner) on the browser,then trouble shooting information.I refreshed Firefox by clicking the refresh Firefox button (this removed my add-ons as well) but after refreshing and restarting my computer I re-installed my only add-on -ad block plus (took 30 secs) then I was able to log in to e bay and operate account/navigate site.

This may/may not assist you, however all has been good with my account for the last 7 days.I use Windows 7.