Vista Home Premium won't Restart, Just Hangs

My system has developed a problem restarting. Whether I use the start button
restart or my desktop shortcut, it goes through the restart fine up to the
shutdown screen. Then it shutsdown but won't reboot. It just hangs with the
monitor off and the system running. I can't seem to figure it out. Google
search comes up with similar but not the exact problem.
Thanks....................