title: GNU screen - cannot enter command mode in a Putty session
body: <p>Opening a shell session on a Linux Red-Hat 5 system, using Putty over ssh, I launch a screen session, but I find that when I press <kbd>CTRL</kbd>+<kbd>A</kbd> that I do not see the command prompt. All other screen commands work fine, apart from this one.</p>
  
  <p>This appears to me to be a problem specific to the combination of Putty and screen, as it worked with other terminal emulators. Has anybody else come across this?</p>