TV tuner amd MCE not full screen

I have a Dell XPS One 2710 with TV tuner in it, purchased about 10/12/12. I can’t get a full screen display watching TV. Regular non-TV display is fine. The TV display shows as a 19 inch diagonal inset on 27" screen. It is connected via coax from the set-top box (Cisco ISB7000) supplied by Hawaiian Telcom to the tuner card. Using Media Center’s auto setup fails. Manual setup does not find any Cisco in its 300+ boxes listed. Hawaiian Telcom, the TV service provider, had no one capable to deal with the problem and sent a Supergeek tech at their expense. He did get a display going but it only shows the 19” inset. I think he tried some of the boxes in the Media Center list till he found something compatible enough to get the display. He was not able to get a full 27” display. Any solution or advice please.

I've got a Hauppage WinTV-HVR-1250 that displays on a 22' LG E2242T-BN Flat Panel. The only way I can get full screen in Media Center is using the Zoom function. When I do that though part of the image can end up off screen. When I go to my cable boxes menu it becomes too big and parts of it are hidden off screen. Using the WinTV app that came with my TVtuner card is fine though, it automatically adjust to make best use of the screen.

Thank you alphanumeric for your reply. Yes, the zoom is not acceptable. The computer came with AVerMedia H339 Hybrid Analog/ATSC/QAM Internal TV Tuner Minicard. Dell tech support tried without success to get a full screen display. They said it is probably not getting a full HD signal to the card from the set top box and that I should use a better coax for this connection. I'm not sure i believe that. Also told me i could connect via the HDMI ports and still use MCE. I like to have the TV in a separate adjustable window so i can do other things at the same time. The cable company says that TV in the MCE window would not be possible with the HDMI connection. It would be either/or. I guess there is no solution

I don't know why HDMI wouldn't work? That doesn't make sense to me? I'd try it anyway if I had it. My monitor is currently connected to the motherboards VGA port. I have plans to upgrade this PC's video card. When I do its current video card will go in my MC PC and I'll switch the monitor to DVI. Right now I use WinTV for watching and recording TV and MC for everything else. It would have been nice to do it all in the one program though. I can do it all with the remote so its not that big a deal.

Thanks for the info, I connected an HDMI and now get a great picture. Just cannot decrease window size like when using Media Center. It's tv only with HDMI but at least i get a very nice full screen picture.