Have you ever experienced that when you are typing something using your keyboard and the character that displays on the screen will be different. For example, when typing in sticky notes, the keyboard does not type the correct character. when you try to type something in quotes, you will get a funny looking e instead of a ".
This is not new actually, when an untrusted software is installed or may be when a driver is corrupt this problem can occur.
If this happens only to your user account in the system, then delete the user account by backing up the data and then create a new user account with the backup data. Again, its not actually a fix for the solution, but it will be much simpler when you are not a computer geek.
Well, May be, you had done any changes to the computer prior to the issue. If you remember any thing, try to undo those changes, if you are not sure, try system restore to the earlier version. please check the link Using System Recovery Options In Windows 7 to know how to use System restore in Windows 7
I would recommend you to perform System Restore to the point where it was working fine and check if it helps. View the following link to perform System Restore.