I've found my Windows Server 2008 std down. The event Log reported:
The process C:\Windows\system32\winlogon.exe (Server) has initiated the power off of computer Server on behalf of user NT AUTHORITY\SYSTEM for the following reason: No title for this reason could be found Reason Code: 0x500ff Shutdown Type: power off
What does this mean? The server has worked well for month, and after the start is working well without any error.