If you want to open multiple form using single button then, your form name needs to be like this..form1,form2,form3 or I can say.. frmwindow1,frmwindow2.. Means form name must be same before numeric in last.
try this,
I am hoping your that button is on Mdi parent form for better visualization.
In your button click event insert this code.
i=i+1
call ViewChildForm("Form" & i)
and define viewchildform as follow,
Private Sub ViewChildForm(frm As Form)
frm.MdiParent = Me
frm.Show()
End Sub
Here I consider, your all form names starts with Form and end with sequence of number.
like form1,form2,form3 etc.
I define i as integer publicly in that MDI parent form. with initial value=0.
Use this logic.