jumping green dots on 42" plasma

Hi my brother has a 42 inch plasma and when you first turn it on you see these little green dots bouncing around on the screen. This happens for about a half hour then seems to go away like it warms up or something. The tv is a four year old zenith, is it just going out?

 

Sounds like it.

 

Isn't that a little quick for a plasma to go out or is that normal.

 

Sometimes we get a dud.