Temperature Controlled fan using arduino project regarding - LCD not displaying anything
Your constructor doesn't match your wiring:

LiquidCrystal lcd(7, 6, 5, 4, 3, 2);


You have:

RS = 7
E = 6
D4 = 5
D5 = 4
D6 = 3
D7 = 2


Yet your wiring has:

RS = 2
E = 3
D4 = 4
D5 = 5
D6 = 6
D7 = 7


I.e., completely backwards.

The constructor prototype is:

LiquidCrystal(rs, enable, d4, d5, d6, d7) 


Yet you seem to have chosen to ignore (or misunderstand) that.

Instead you need to specify your pins correctly:

LiquidCrystal(2, 3, 4, 5, 6, 7);


Also, as a side note, you don't have a ground connection to that little 9V circuit off to one side - so you will never be able to control it.  Read this.