that can be one of the reasons why.
possibly because you may have too many startup programs when you log in loading, and too many background programs when you are shutting down.
try.. for logging in.
when you have already logged in. go to
start>run> type in "msconfig" w/o quotes
move over to the startup tab at the right end and uncheck any unneccary programs you dont want to start up.
if you have no clue what they are, expand the "command" column so that it shows the directory and you can possible get an idea at the folders it is coming from.
for shutdown..
if you are willing, read this article.
http://www.tweakxp.com/article36963.aspx