Problem in checking empty point

Please someone help me . I want a picturebox to move form one point to another point (Drag n Drop) and I want to know how to check whether the point is empty or not. if empty movable otherwise move to another empty point.
I have managed to make two player drag and move turn by turn but I can`t figure out how to check the point

Thank You

    Dim NextMove As Boolean
    Dim MouseIsClicked As Boolean
    Dim LeftSet As Boolean
    Dim TopSet As Boolean
    Dim HoldLeft As Integer
    Dim HoldTop As Integer
    Dim LetLeft As Integer
    Dim LetTop As Integer 



Dim RowA As Point() ={New Point(40, 40), New Point(140, 40), New Point(240, 40), New Point(340, 40), New Point(440,40)}






Private Sub PictureBox1_MouseUp(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseUp
        MouseIsClicked = False
        LeftSet = False
        TopSet = False
        NextMove = False

	First Row of Board
        If sender.left <= 90 And sender.top <= 90 Then
            PictureBox1.Location = RowA(0)
        End If

        If sender.left > 90 And sender.left <= 190 And sender.top <= 90 Then
            PictureBox1.Location = RowA(1)
        End If

        If sender.left > 190 And sender.left <= 290 And sender.top <= 90 Then
            PictureBox1.Location = RowA(2)
        End If

        If sender.left > 290 And sender.left <= 390 And sender.top <= 90 Then
            PictureBox1.Location = RowA(3)
        End If

        If sender.left > 390 And sender.left <= 490 And sender.top <= 90 Then
            PictureBox1.Location = RowA(4)
        End If

	Label2.Text = (" Player 2`s Turn")
        NextMove = True


    End Sub

    Private Sub PictureBox1_MouseDown(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseDown
        If NextMove = False Then
            MouseIsClicked = True
        End If


    End Sub

    Private Sub PictureBox1_MouseMove(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseMove
        ' check for mouse clicked?
        If MouseIsClicked = True Then

           
            HoldLeft = (Control.MousePosition.X - Me.Left)
            HoldTop = (Control.MousePosition.Y - Me.Top)


            If LeftSet = False Then
                LetLeft = HoldLeft - sender.left
                LeftSet = True
            End If

            If TopSet = False Then
                LetTop = HoldTop - sender.top
                TopSet = True

            End If

           
            sender.left = HoldLeft - LetLeft
            sender.top = HoldTop - LetTop

        End If
    End Sub

Private Sub PictureBox2_MouseUp(sender As Object, e As MouseEventArgs) Handles PictureBox2.MouseUp
        MouseIsClicked = False
        LeftSet = False
        TopSet = False
       
        'First Row of Board
        If sender.left <= 90 And sender.top <= 90 Then
            PictureBox2.Location = RowA(0)
        End If

        If sender.left > 90 And sender.left <= 190 And sender.top <= 90 Then
            PictureBox2.Location = RowA(1)
        End If

        If sender.left > 190 And sender.left <= 290 And sender.top <= 90 Then
            PictureBox2.Location = RowA(2)
        End If

        If sender.left > 290 And sender.left <= 390 And sender.top <= 90 Then
            PictureBox2.Location = RowA(3)
        End If

        If sender.left > 390 And sender.left <= 490 And sender.top <= 90 Then
            PictureBox2.Location = RowA(4)
        End If

        NextMove = False
        Label2.Text = ("Player 1`s Turn")

    End Sub







    Private Sub PictureBox2_MouseDown(sender As Object, e As MouseEventArgs) Handles PictureBox2.MouseDown
        If NextMove = True Then
            MouseIsClicked = True
        End If

    End Sub

    Private Sub PictureBox2_MouseMove(sender As Object, e As MouseEventArgs) Handles PictureBox2.MouseMove
        ' check for mouse clicked?
        If MouseIsClicked = True Then

           
            HoldLeft = (Control.MousePosition.X - Me.Left)
            HoldTop = (Control.MousePosition.Y - Me.Top)


            If LeftSet = False Then
                LetLeft = HoldLeft - sender.left
                LeftSet = True
            End If

            If TopSet = False Then
                LetTop = HoldTop - sender.top
                TopSet = True

            End If
            sender.left = HoldLeft - LetLeft
            sender.top = HoldTop - LetTop

        End If
    End Sub