Hi,
Did you run and try the PID_Relay example before modifying it?
Before the dislplay and buttons were added.
If not, then I suggest you load the example and get it going first.
Use a potentimeter on the A0 analog input.
Then when you get that working, add the thermocouple and get that working.
Use Serial Monitor to see your variables.
Then and only then when you have that working, add the display.
Tom.. 