Hi,
Not sure if these suggestions can help and hopefully others have more information if they don't.
1. Try an external USB keyboard with those same symbols if available to see if the problem may be related to the internal notebook keyboard.
2. Try in Windows Safe Mode to help confirm if it is a software issue.
3. Don't imagine your keyboard language in Windows would change without you knowing it, but something else to check.
4. Go back to an earlier Windows System Restore point when everything was working if you're not worried about losing any changes since then?
5. Consider checking with your local ASUS support to see if they know more about it?
http://www.asus.com/support/CallUs
Good luck!