will i harm my plasma tv by keeping it on all nite? will it shorten the life of my tv?

Earlier models are susceptible to screen burn-in and image retention (however, newer models have green phosphors and built-in technologies to eliminate this, such as pixel shifting)

Also Phosphors in older models lose luminosity over time, resulting in gradual decline of absolute image brightness (newer models are less susceptible to this, having lifespans exceeding 60,000 hours, far longer than older CRT technology)

The worst thing that can happen is you get screen burn.

With phosphor-based electronic displays (including cathode ray and plasma displays), the prolonged display of a menu bar or other static (fixed in place and unchanging) graphical elements over time can create a permanent ghost-like image of these objects since phosphor compounds which emit the light lose their luminosity with use. As a result, when certain areas of the display are used more frequently than others, over time the lower luminosity areas become visible to the naked eye and the result is called burn-in. While a ghost image is the most noticeable effect, a more common result is that the image quality will continuously and gradually decline as luminosity variations develop over time, resulting in a "muddy" looking picture image. Most plasma display producers state a 100,000 hours time before brightness halves, theoretically allowing for over ten years of normal viewing before the display dims significantly.

yes it will if you want it to blow out so your parents can buy you another one(bigger better one)