Congrats on Your Purchase! What you see when TV is turned on is, INFO of Time and, the 720x480 is the *Resolution* of what is being displayed. Your purchased set IS capable of displaying a "native" Resolution of, 1920x1080p. So no need to panic. I won't get too involved in what Resolutions are, just to keep as simple as possible for you..but keep in mind the LAST set of numbers..ie:"x480"..is whats most important! I'll assume your set IS connected to a Cable or Satellite Converter Box via HDMI or COMPONENT Cables.
The ONLY time you will see FULL dispay of 1080p is when watching HD, and/or, Blu-Ray DVDS, via HDMI/Component cables. Broadcast Analog, Digital and High-Definition television channels..via your Cable or Satellite Providers..are displayed as x480p, x720p and/or x1080i. Did you notice the letter "i" after 1080..and NOT the letter "p"? "i" = Interlace and "p" = Progressive. Again..remember that only HD/Blu-Ray DVDs are displayed in 1080p.
I will again assume, that when you turned on your set, your Cable/Sat Converter was tuned onto a, *Analog or Digital Broadcast Channel*. These Channels are broadcast in 720x480p.
If you subscribe to/for *High Definition Broadcast Channels*, you should have a High Definition Converter Box. Your Cable or Satellite technician, if knowledgeable and courteous, should have asked you when installing your service, what Resolution you preferred when viewing High Definition broadcasts/channels. Here your ONLY choices would either be in, 1280 x 720p..or..1920 x 1080i. This decision is dependent of your viewing choices. I enjoy FAST MOVING/ACTION PACKED broadcasts such as, Hockey/Football/Boxing/Martial-Arts and Movies..so I prefer the 'smoother' picture/Resolution that 720p offers, other than the "jagged" picture/Resolution, I and others see watching such broadcasts with 1080i. Again..this is the viewers choice, so I recommend you watch YOUR favorite Hi-Def broadcasts in both resolutions of 720p and 1080i, and decide which is best for your viewing pleasure.
In regards to 480i, 480p, 720p, 1080i and 1080p *RESOLUTIONS*..go to CNETS 'Tips & Tricks' and in the Search Box, type..HDTV: Know your high-res options
Thats a good starting point in explaining more in-depth about *Resolutions*. Hope this helped..not confused you more..in understanding what the 720 x 480 means?