GTX 260 Resolution on Samsung TV

At present I use my 26" Samsung TV as my PC monitor, this has never been a problem in the past when using the standard style of connector but when I got my new computer a few months back with a GeForce 260GTX card I have been unable to get it to display correctly through my Samsung TV when using a HDMI conversion cable, When I say display correctly I mean the resolutions don't seem to match up so I have either a small picture inside of the viewing area or a picture that is blown up to big meaning I cant see everything on screen. Does anyone know what the possible problem is and how i would be able to fix it as its driving me mad knowing I have the option to display my PC through HDMI but my GPU and TV don't want to get along!

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