Windows Vista Shutdown in Vista Home Premium takes forever

When I select shut down, it shows "Windows is shutting down" for about 15 minutes and then goes to re-login..I then click on the bottom right and select shut down again and it does. What can I check to speed up the process?
Thanks

 

To check if a particular program is slowing the machine when you shut down, e.g. an antivirus program, go to Control Panel > Classic View > Performance Information and Tools > Advanced Tools (in the left pane). The problem is sometimes shown on this screen, although you may have to click Advanced tools in the left pane then View performance details in the Event log.

If the problem isn’t shown, click the Windows Orb (Start) > All Programs > Accessories, right-click Command Prompt then ‘Run as Administrator’. Copy & Paste or type wevtutil qe Microsoft-Windows-Diagnostics-Performance/Operational /f:text > %userprofile%\Desktop\Event.txt (note the five spaces) and press Enter. If you Copy & Paste the command, use mouse right-click to Paste it into the prompt. Close the command prompt and double-click Event.txt on the Desktop to open it. Go to the end of the file (Ctrl+End) to see the most recent events. Those with an Event ID in the 200 series are shut down events. There may be a name or reason in the event listing.