Can't Go Beyond The Welcome Screen When I Bootup

Please help. I can't access certain computers. What happens is that when I boot up it welcomes me and shows the logon screen. when I click on the user account so that I can either just enter or type a password nothing happens. It does not show the password field and all it shows is loadind your personal details and then it says saving personal details and thats it, It just stays on the logon screen so I am locked out of the computer. Please help. I am desperate.