hi..well first you need to create a table in database to be able to maintain the users who can log in...
in your application connect to the database and try the following code at your Login button..

OleDbConnection con = new OleDbConnection("Provider=Microsoft.Jet.OLEDb.4.0; Data Source=F:\\QMGT.mdb;");
OleDbCommand com = new OleDbCommand("select UserId,Password From Users", con);
OleDbDataReader rd;
con.Open();
rd = com.ExecuteReader();
if (rd.HasRows)
{
while (rd.Read())
{

string s1 = rd[0].ToString();
string s2 = rd[1].ToString();
if (s1 == txtUserID.Text && s2 == txtPassword.Text)
{
Response.Redirect("Default2.aspx");
}
else
{
Label1.Text = "UserID,Password does not match Please Try again!!";
}
}

you dont even need code for login. on the tool box you have createuserwizard and the others. use them instead.