Help,my friends computer which is running windows xp wont go past log in page,when you click on icon it momentally say,s loading your personal settings then immediatleyl logs off,If I use control-alt-delete it brings up the password box(which was previously not used).If I say ok it comes up with incorrect password.He is using an anti virus system called Panda!.Any help for beginners would great,cheers.

Try using The last known good configuration option.

try pressing f8 at boot up that will get you in or as bear said system restore