'API调用与常用定义：
Private Declare Function SystemParametersInfo _
  Lib "user32" _
  Alias "SystemParametersInfoA" _
   (ByVal uiAction As Long, _
    ByVal uiParam As Long, _
    pvParam As Any, _
    ByVal fWInIni As Long) As Boolean
 
Private Const SPI_GETSCREENSAVEACTIVE As Long = &H10  '屏保是否启用的常量
Private Const SPI_GETSCREENSAVERRUNNING As Long = &H72 '屏保是否运行的常量

Private Sub Timer1_Timer()
  Dim bRunning As Boolean   '屏保是否运行的变量,当然你可以定义全局变量
  SystemParametersInfo SPI_GETSCREENSAVERRUNNING, 0, bRunning, False '调用API,bRunning返回屏保运行状态
  Debug.Print Time; "屏保运行="; bRunning '演示:打印屏保是否运行的信息
End Sub
 
'另外,查看屏保是否启用,也可以用下面方法:
SystemParametersInfo SPI_GETSCREENSAVEACTIVE, 0, bActive, False 'bActive为返回值(逻辑型)

Option Explicit
Private Declare Function GetLastInputInfo Lib "user32" (plii As LASTINPUTINFO) As Boolean
Private Declare Function GetTickCount Lib "kernel32" () As Long
Private Type LASTINPUTINFO
  cbSize As Long
  dwTime As Long
End Type
 
Private Sub Form_Load()
   Timer1.Interval = 1000  
End Sub
 
Private Sub Timer1_Timer()
  Dim lii As LASTINPUTINFO
  lii.cbSize = Len(lii)
  If GetLastInputInfo(lii) Then
    If (GetTickCount - lii.dwTime) / 60000 >= 15 Then      
      Call MsgBox("由于本机15分钟没有操作，如果3分钟后没有反应，系统将强制关机", vbYesNo + vbExclamation + vbDefaultButton2, "提示")
    End If
  End If
End Sub