I dont think you account is highjacked.If you think so, just go to your yahoo account setting and change your password.

Well the problem could be :

your browser is not checking for new version of web page :

on iexplore click on

tools

internet options

click on settings

and make sure the radio button on every visit to the web page in ticked

also on intenet options

click on delete files to clear the old files.

hope this works.

Dr_Evil