tv aspect changing on tv problem,cant see full screen

dont know quite this belongs,so i put it in this section

i just bought a new panasonic 37" plasma tele,
http://www.electricaldiscountuk.co....22&PHPSESSID=4844414ac1baabcf4ee65c3a078770bc

problem is,i am still having problems with the aspect ratio (i guessing its related to that),
i sometimes still cant see the full width of the screen
when i put a sky channel on,the screen size,with the "sky channel" info box looks ok,and sometimes,on movies i have a black border running across the top/bottom..but then after a few seconnds or so,it jumps to full screen,black border gone,sky info box now at bottom of page,and still i have the problem of not seeing all the screen side to side (more noticable when text appears,thus cant read it all.

this happened on me old tele,and just thought because it was an old banger,and wasnt widescreen,this being the reason for the screen chop

i am from the u.k

happy new year folks