hmm... have you cleaned your kybd lately?
no crumbs, ashes, tobacco, food, or other foreign material under the ~key?
dust buster vac, or canned air might do the trick if there is.
have you ever had any overheating issues?
do you have a laptop cooler under it?
(just wild specualtions, but you never know)
another thing you can try, but be very, very gentle when you do...
pop that key out, and clean under it. use a cotton swab (q-tip).
use a clean cotton swab (q-tip) to press the pad underneath, and see if the key is working, in a program like notepad.
if it is working in notepad, put the key back in, and try it in game.
I do this every few months, because I practically live at my computer,
and my kybs always get gunked up. even my laptop.
