Grey bar at the top of the page... Answered
Today was for first time this happened to me (note: at this machine, the OS is WinXP, and so the browser being MSIE can not be upgraded higher than 7). the grey bar near the top of the page (where SIGN IN is slightly higher in the right hand corner), prevented me from signing in. The drop down box slid behind the grey line. I only managed to get a sign on screen by trying to post here (and then it of course, prompts you to sign in or join).