Microsoft Installation slow to reboot

Running WP Multisite on Server 2008. No complaints until recently that when the server is rebooted that it can be over 15 minutes before the WordPress sites come back on-line. Haven’t found anything that will leave me to a conclusion. I have played with the plug-ins without any impact. I watch the Windows Task Manager and I don’t see any real performance issues. Any recommendations for something to look at to boost the initial load time?