Ummm... MyPosition never changes even though you change the xPos and yPos vairables. You have to create a NEW Point with the new values of xPos and yPos every time you execute this Click event handler.
Come to think of it, you don't even need MyPosition at all.
Using bmp As New Bitmap(1, 1)
xPos = 130
yPos = 100
Using g As Graphics = Graphics.FromImage(bmp)
g.CopyFromScreen(New Point(xPos, yPos), New Point(0, 0), New Size(1, 1))
End Using
End Using