Click on Tools, then Junk E-mail Options. If you have a blue dot
in one of the lower two circles, click on a higher circle and then Apply.
click on OK.
Most Norton antivirus programs tend to cause various problems in Window
Mail, although seldom immediately. So do most McAfee antivirus programs
or a recent one from Trend. These need to be uninstalled, not just
disabled,
to stop them from causing these problems.
You may want a replacement antivirus program, such as avast! or AVG.
Either of these should have a custom install that tells it to leave out the
part that scans email.