Why does loop doesnt stop at .showdialog in formloadevent - vb.net

Question

Hello here is a very strange bug I cannot solve. I have a while loop in my formload that looks this way :
While loginOK = False And pstop = False
LoginForm1.ShowDialog()
If NewReg = True Then
While RegErfolgreich = False
Registrierung.ShowDialog()
Dim con As New SqlConnection(My.Settings.SLXADRIUMDEVConnectionString)
con.Open()
Dim cmd = New SqlCommand("Insert Into sysdba.PL_Userverwaltung (Benutzername, Passwort, [E-Mail-Adresse], Profil_OK) Values('" & RegBenutzername & "', '" & RegPassword & "', '" & RegEMailAdresse & "', 'f')", con)
If cmd.ExecuteNonQuery() = 1 Then
My.Settings.Benutzername = RegBenutzername
My.Settings.Passwort = RegPassword
My.Settings.Save()
Me.Close()
RegErfolgreich = True
Else
MsgBox("Es ist ein Fehler aufgetreten.")
End If
End While
Else
NewReg = False
End If
End While
The problem is that after closing loginform1 he jumps back in the loop, and when he starts looping again he opens loginform1 and closes it instantly. and loops again in the while loop.
That means I have a endless loop, which shows the loginform1 and closes it a millisecond later.
One thing to mention is that a friend of mine opened my project in an older vs studio version and this mysterious bug doesnt happen??
Hope for input cheers
EDIT:
Here is loginform1 code
Private Sub OK_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles OK.Click
If UsernameTextBox.Text <> "" And PasswordTextBox.Text <> "" Then
Startseite.LoginUsername = UsernameTextBox.Text
Startseite.LoginPassword = PasswordTextBox.Text
Startseite.loginOK = True
Me.Close()
Else
MsgBox("Bitte Benutzername und Passwort eingeben!")
End If
End Sub
Private Sub Cancel_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Cancel.Click
Startseite.pstop = True
Me.Close()
End Sub
Private Sub LoginForm1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
If My.Settings.Benutzername <> "" And My.Settings.Passwort <> "" Then
'MsgBox(My.Settings.Benutzername & " " & My.Settings.Passwort)
UsernameTextBox.Text = My.Settings.Benutzername
PasswordTextBox.Text = My.Settings.Passwort
End If
End Sub
Private Sub lblNeuRegistrieren_Click(sender As Object, e As EventArgs) Handles lblNeuRegistrieren.Click
Startseite.NewReg = True
Me.Close()
End Sub

Answer 1

About your error, probably you didn't initialize your startseite variable to be your main form, loginOK And pstop never get changed and that's why the loop never stops. But on the rest of your code, some general tips.
This is unnecesary
If NewReg = True Then
''
Else
NewReg = False
End If
If NewReg is not true, then it's false by definition. Should be
If NewReg Then
''
End If
Also, overloading the showDialog on loginForm1 is a better solution than adding a yourmainclass object on the second form. It is easier to debug and provides better reusability.

Answer 2

try exiting loop on message box
If cmd.ExecuteNonQuery() = 1 Then
My.Settings.Benutzername = RegBenutzername
My.Settings.Passwort = RegPassword
My.Settings.Save()
Me.Close()
RegErfolgreich = True
Else
MsgBox("Es ist ein Fehler aufgetreten.")
Exit While
End If