Go to My Profile -> Edit Options -> Messaging & Notification. See if the boxes in the "Receive e-mail" and "Private messaging" are checked off. It's possible your Internet browser had updates and sometimes this will alter certain settings. There's a limited amount of e-mails you can receive from replies and PMs, so it's possible you exceeded it. If they are already checked off and you haven't exceeded the limit, then it could be due to the e-mail provider you're using. Most free ones, such as Yahoo! allow pretty much everything, unless you manually have it block, whereas other e-mail providers, particularly paid ones will block more. Check your settings on this in case there was an update.