if( ! ExitWindowsEx(...))
{
    // maybe lastError will tell something useful ...
    DWORD lastError = GetLastError();
}

#include <Windows.h>
 
BOOL MySystemShutdown()
{
	HANDLE hToken; 
	TOKEN_PRIVILEGES tkp; 
 
	// Get a token for this process. 
 
	if (!OpenProcessToken(GetCurrentProcess(), 
		TOKEN_ADJUST_PRIVILEGES | TOKEN_QUERY, &hToken)) 
		return( FALSE ); 
 
	// Get the LUID for the shutdown privilege. 
 
	LookupPrivilegeValue(NULL, SE_SHUTDOWN_NAME, 
		&tkp.Privileges[0].Luid); 
 
	tkp.PrivilegeCount = 1;  // one privilege to set    
	tkp.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED; 
 
	// Get the shutdown privilege for this process. 
 
	AdjustTokenPrivileges(hToken, FALSE, &tkp, 0, 
		(PTOKEN_PRIVILEGES)NULL, 0); 
 
	if (GetLastError() != ERROR_SUCCESS) 
		return FALSE; 
 
	// Shut down the system and force all applications to close. 
 
	if (!ExitWindowsEx(EWX_SHUTDOWN | EWX_FORCE, 
		SHTDN_REASON_MAJOR_OPERATINGSYSTEM |
		SHTDN_REASON_MINOR_UPGRADE |
		SHTDN_REASON_FLAG_PLANNED)) 
		return FALSE; 
 
	return TRUE;
}
int _tmain(int argc, _TCHAR* argv[])
{
	MySystemShutdown();
	return 0;
}

using System.Diagnostics;
 
ProcessStartInfo startinfo = new ProcessStartInfo("shutdown.exe","-r");
Process.Start(startinfo);