How to disable the Ctrl-S (XOFF) keystroke in Putty
If you are connecting your server or desktop through putty and if you press Ctrl-S accidentally it will send Xoff the only way to recover is by pressing Ctrl-Q.
If you want to disable this use the folloing commands from your terminal
echo "stty -ixon" >> ~/.bash_profile
For more options check stty man page from here
Thank to richard for this tip.