Try this...

Private Sub Command1_Click()
On Error Goto Err_OpenForm

Dim Mypwd As String


Mypwd=Inputbox("Enter Your Password")

If Mypwd<> "YourPassword" Then
Exit Sub
Else
Docmd.OpenForm, "FormName"
Endif

Exit_OpenForm:
Exit Sub
Err_OpenForm:
Msgbox Err.Number & " ; " & Err.Description
Resume Exit_OpenForm

End Sub