Creating a user registration form

How should I go about creating a registration page in Windows forms? I can easily create a registration page, but I'm not sure if it's the best way. I'd have a service account that is hard coded, and it creates entries in a user table. I don't like to hard code passwords, but I don't know of another way. I guess in every case I'd end up having to hard code a password, right? I do have SSL enabled, and I've Wiresharked it and was unable to read any of the traffic.

Here's a simplified example of some code I wrote a while ago:

Public Class Registration
Dim connStr As String = "server=domain.com; port=3306; user id=userid;password=password;database=db;SslMode=Required;"
Dim msc As New MySqlConnection

Private Sub registerBTN_Click(sender As System.Object, e As System.EventArgs) Handles registerBTN.Click
            Dim dr As MySqlDataReader
                dr = checkUsername.ExecuteReader()
            Dim match As Boolean = False
            While dr.Read()
                If dr("Username").ToString = usernameTXT.Text Then
                    match = True
                    Exit While
                End If
            End While
            dr.Close()
            If match = False Then
                Dim User_GUID As Guid = New Guid
                User_GUID = Guid.NewGuid()
                Dim Encrypted_Password As String = Encryption(passwordTXT.Text, User_GUID.ToString)
                    Dim mscCMD As MySqlCommand = New MySqlCommand("INSERT INTO Users (Username, UserID, Password, Profile, Email) " & _
                                                                      "VALUES (@uname, @id, @pwd, @url, @mail)", msc)
                    With mscCMD.Parameters
                        .AddWithValue("uname", usernameTXT.Text)
                        .AddWithValue("id", User_GUID.ToString)
                        .AddWithValue("pwd", Encrypted_Password)
                        .AddWithValue("url", urlOptTXT.Text)
                        .AddWithValue("mail", emailTXT.Text)
                    End With
                    mscCMD.ExecuteNonQuery()
                MsgBox("Registration successful!", MsgBoxStyle.Information)
                My.Settings.First_Run = False
                Me.DialogResult = Windows.Forms.DialogResult.OK
                Me.Close()
End Sub

Private Sub Registration_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Try
            msc.ConnectionString = connStr
            msc.Open()
        Catch ex As MySql.Data.MySqlClient.MySqlException
            Me.Close()
        End Try
    End Sub

I want to know if this is a good approach. Does this have any vulnerabilities? Is there a better way to create a user registration method?

Also, here's my encryption/decryption.

Public Function Encryption(ByVal Plaintext_Password As String, ByRef User_GUID As String) As String
    Dim guidANDPassword As String = User_GUID.ToString + Plaintext_Password
    Dim shaobj As New Security.Cryptography.SHA1CryptoServiceProvider
    Dim guidPwdBytes() As Byte = System.Text.Encoding.ASCII.GetBytes(guidANDPassword)
    guidPwdBytes = shaobj.ComputeHash(guidPwdBytes)

    Dim Encrypted_Password As String = String.Empty

    For Each b As Byte In guidPwdBytes
        Encrypted_Password += b.ToString("x2")
    Next
    User_GUID = User_GUID.ToString()
    Return Encrypted_Password
End Function


Public Function Decryption(ByVal Plaintext_Password As String, ByVal User_GUID As String) As String
    Dim guidANDPassword As String = User_GUID.ToString + Plaintext_Password
    Dim shaobj As New Security.Cryptography.SHA1CryptoServiceProvider
    Dim guidPwdBytes() As Byte = System.Text.Encoding.ASCII.GetBytes(guidANDPassword)
    guidPwdBytes = shaobj.ComputeHash(guidPwdBytes)
    Dim Encrypted_Password_Of_Specified As String = String.Empty

    For Each b As Byte In guidPwdBytes
        Encrypted_Password_Of_Specified += b.ToString("x2")
    Next
    Return Encrypted_Password_Of_Specified
End Function