If you ever accidentally hit CTL-S in Putty, your terminal seems to lock. After a bunch of searching, Pat found an answer for why this happens on an old 2004 mailing list.
"Every time I accidentally press Ctrl+s in Putty when connected to any Linux box via ssh, my session stops responding. How do I restore it?"
The reason:
"This is software flow control - left over from the days of serial connections. Control+S sends XOFF and Control+Q sends XON and together they make XON/XOFF, or "software," flow control. Hardware flow control is known as RTS/CTS and involves switching the signal on a couple of the pins connected to the serial port."
Original Post:
So, when that happens, just hit CTL-Q, and you are running again.
IMPORTANT NOTE: All / Any keys you hit after hitting ctl-s will be BUFFERED and SENT when you hit ctl-q.
MORE IMPORTANT WARNING: Don't send mad/frustrated commands. Because if you hit ENTER, it gets buffered too. All those commands WILL BE SENT and EXECUTED.