Cursor.Position won't work in game, you need to use a Windows API such as mouse_event or SendInput.
Code:
Declare Function mouse_event Lib "user32.dll" Alias "mouse_event" (ByVal dwFlags As Int32, ByVal dX As Int32, ByVal dY As Int32, ByVal cButtons As Int32, ByVal dwExtraInfo As Int32) As Boolean
Private Const MOUSEEVENTF_MOVE As Integer = &H1
Private Sub MoveCursor()
' Set the Current cursor, move the cursor's Position,
mouse_event(MOUSEEVENTF_MOVE, -(Integer.Parse(TextBox4.Text)), -(Integer.Parse(TextBox5.Text)), 0, 0)
End Sub
Hopefully that works, I haven't tested it. Also, use a NumericUpDown control instead of a text box. If someone types a letter into the box the whole thing will crash.