Slow log-on and log-off

Good day to all.


I have a problem with my Dell Inspiron 1721 laptop. From the moment I press the power-up button to the time I can actually run any software it takes approximately five minutes. It has been slowing down a little bit at a time for a while.
Additionally, the log-off process takes at lease 1 1/ 2 minutes.


I am running Vista, use Norton Internet Security package, running a home wi-fi with a links router, 2 gb of memory.

A couple if days ago, I checked my email and there were two messages from "Mail Delivery System" and in the body of the email it said:

################################################## ##################
# THIS IS A WARNING ONLY. YOU DO NOT NEED TO RESEND YOUR MESSAGE. #
################################################## ##################

Your message could not be delivered for 0 days, 4 hours, 0 minutes.
It will be retried until it is 5 days, 0 hours, 0 minutes old.

For further assistance, please send mail to steve@......com 

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

Excessive email sent - Please try again later:
================================================== =====

I am not steve so maybe my PC has been highjacked.
Any help would be greatly appreciated.