Windows 2008 Server R2 turns itself off

Question

I have a Windows 2008 R2 Server that switchs off on his own. and it does not look like a hardware problem since I can see in the log how all services are stopped and after:

Log Name:      System
Source:        Microsoft-Windows-Kernel-Power
Date:          28/12/2011 01:19:49
Event ID:      109
Task Category: (103)
Level:         Information
Keywords:      (4)
User:          N/A
Description:
The kernel power manager has initiated a shutdown transition.

And:

Log Name:      System
Source:        Microsoft-Windows-Kernel-General
Date:          28/12/2011 01:19:50
Event ID:      13
Task Category: None
Level:         Information
Keywords:      
User:          N/A
Description:
The operating system is shutting down at system time ‎2011‎-‎12‎-‎28T01:19:50.956025700Z.

What could be the problem?

UPDATE:

There is no UPS. It is not a virtual machine.

I have switched now from "Balanced" to "high performance" to see what happens.

This is the event sequence:

Information 28/12/2011 01:19:50 Kernel-General  13  None
Information 28/12/2011 01:19:49 Kernel-Power    109 (103)
Information 28/12/2011 01:19:49 Service Control Manager 7036    None
Information 28/12/2011 01:19:48 Service Control Manager 7036    None
Information 28/12/2011 01:19:48 Service Control Manager 7036    None
Information 28/12/2011 01:19:47 Service Control Manager 7036    None
Information 28/12/2011 01:19:47 Service Control Manager 7036    None
Information 28/12/2011 01:19:47 Service Control Manager 7036    None
Information 28/12/2011 01:19:47 Service Control Manager 7036    None
Information 28/12/2011 01:19:47 Service Control Manager 7036    None
Information 28/12/2011 01:19:47 Service Control Manager 7036    None
Information 28/12/2011 01:19:47 Service Control Manager 7036    None
Information 28/12/2011 01:19:47 Service Control Manager 7036    None
Information 28/12/2011 01:19:47 Service Control Manager 7036    None
Information 28/12/2011 01:19:47 Service Control Manager 7036    None
Information 28/12/2011 01:19:47 Service Control Manager 7036    None
Information 28/12/2011 01:19:46 Service Control Manager 7036    None
Information 28/12/2011 01:19:46 Service Control Manager 7036    None
Information 28/12/2011 01:19:46 Service Control Manager 7036    None
Information 28/12/2011 01:19:46 Service Control Manager 7036    None
Information 28/12/2011 01:19:46 Service Control Manager 7036    None
Information 28/12/2011 01:19:46 Service Control Manager 7036    None
Information 28/12/2011 01:19:46 UserPnp 20010   (7010)

Before the UserPnP event, there is an event from 4 hours before. All those "7036" are "the XXX service entered stopped state"

Probably it does not explain anything, but this is the UserPnp event:

Log Name:      System
Source:        Microsoft-Windows-UserPnp
Date:          28/12/2011 01:19:46
Event ID:      20010
Task Category: (7010)
Level:         Information
Keywords:      
User:          SYSTEM
Description:
One or more of the Plug and Play service's subsystems has changed state. 

PlugPlay install subsystem enabled: 'false' 
PlugPlay caching subsystem enabled: 'false' 

Answer 1

Usually this is due to automatic updates. Both the 109 and 13 Event IDs can indicate a reboot. Look for update messages in the event log from WindowsUpdateClient, for example:

...

Also, if someone pressed the power button that can initiate a graceful shutdown with many systems.

Answer 2

Probably not the answer but a contribution. Found the same error in a couple of virtual servers, after an uptime alarm, and could see all services being stopped nicely and found that 109 was an entry after a planned reboot from Citrix service event ID 1074

Log Name:      System
Source:        USER32
Event ID:      1074
Task Category: None
Level:         Information
Keywords:      Classic
User:          SYSTEM
Description:
The process C:\Program Files (x86)\Citrix\System32\Citrix\Ima\IMAAdvanceSrv.exe 
               has initiated the restart of computer <COMPUTERNAME> 
               on behalf of user NT AUTHORITY\SYSTEM for the following 
               reason: Application: Maintenance (Planned)
 Reason Code: 0x80040001
 Shutdown Type: restart