scheduled tasks appearing to run, but don't

I have XP home on a 2.4 ghz, 512 MB Toshiba laptop, with SP2 installed. Not
long ago, I noticed that the scheduled tasks appear to start, and appear to
end, but they don't appear to really be running.

Though the task logs shows these as starting and stopping, I get messages
from the various tasks that they haven't run in quite sometime. For example,
I have a weekly scan set up for Norton Anti-Virus. It seems to start up at
the appropriate time, but when I check for my last system scan within the
program, it's been a few months, unless I've done it manually.

Can anyone help?