I'm running a fresh install of ubuntu 14.04 and I've got a strange problem. When I login to the GUI I successfully get to my desktop and can use everything fine, but as soon as I try to sudo anything, it does not accecpt my password. I also cannot use the GUI to change my password as when I enter my existing password, it says it is incorrect. Also, if I lock my machine and try to log back in it claims my password is incorrect, but if I hit the switch user option and choose the same account, I can then enter my password and I get back in.
Any ideas what is causing this?