sorry for the spelling I am dislex.....
Some things to try;
3 ways to RESET
1) in the "Custom Settings Menu" the first item is "RESET"
2) hold the +- and AF buttons for more than 2 seconds
3) turn camera off remove the battery 10 seconds , replace battery and turn on.
4)press the reset switch next to the DC in, USB and Video out ports.
if none of the above work then there is a hardware problem.
As for trade depending on where you trade (if the place fixes cameras) then there may or may not be a lose in how much you get.
I'm not shoure tradeing for a D90 would be much of a upgrade and it may be cheeper to get the D80 fixed and continu using it or a year or 2.