WordPress Database Upgrade Screen

My 2.7 installation was working fine until a couple of hours ago. I tried to log back in and I keep getting a page which says the above and tells me to upgrade by pressing the button. When I do that it tells me that the upgrade was successful despite a load of error messages, and I get another button to click on which gets me right back where I started from. I have also had to reset my password because it wasn’t accepting mine. Could I have been hacked or something?