Are there any buttons on the tv or remote to change the aspect ratio or zoom? or auto-adjust/reset setting?
Maybe that will work here.
As for the resize greyed out, it might be another setting that is overriding the ability to scale. you could try resetting the graphic options to default as well to see if it comes back.
Also, are you using two monitors? or just the HDTV?
Also, is this a laptop? or what card do you have in your PC?