Windows XP shutdown issue

Hi. I have an HP Pavillion 505n with Windows XP Home SP2, 2.20ghz Celeron, with 256mb Ram. When I click on the start menu, and select shutdown, the system will hang for about five minutes, then the shutdown dialog box will appear and I can turn off the machine. If I use ALT+CTRL+DEL and get into the task manager, and use the shutdown menu from there, the machine doesn’t hang at all; it shuts down correctly. I have run Spybot S&D, Norton AV, and AVG anti-virus, all with the most recent definitions. Is this a Windows issue that I’m not aware of? If anyone has any ideas, I’d appreciate the input. Thanks in advance!

~J