I own an insignia 42"

The TV resolution is set by the video sources, not at the TV, in this case, your Dish network box is the one that is sending out 480p so the TV will display what it is being fed with.
What does Dish TV say aboyt this problem? How about the setup menu on the Dish network box?
Your TV works the same as your PC monitor, except that your monitor does not have a tuner, you adjust the resolution at the PC not at the monitor. 480p in = 480p display.

Please leave rating if it helps.

Basic LCD monitor and TV troubleshooting guide:
http://www.fixya.com/support/r5093881-lcd_flat_panel_tv_troubleshooting_guide
http://www.fixya.com/support/r6150077-basic_lcd_monitors_troubleshooting
http://www.fixya.com/support/r7406380-tv_training_manuals
Failed TV and Monitors: http://s807.photobucket.com/albums/yy352/budm
Learn about bad caps: http://en.wikipedia.org/wiki/Capacitor_plague