VB.NET Code behind:

PrivateSub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim dbconn As SqlConnection
Dim dbcommand As SqlDataAdapter
Dim dslogin As New DataSet
dbconn = New SqlConnection("Server=localhost;UID=sa;PWD=sa;database=websiteDemo")
dbcommand = New SqlDataAdapter("Select UserID from " _
& "Login Where " _
& "Username = '" & TextBox1.Text _
& "' and Password = '" & TextBox2.Text _
& "'", dbconn)
dbcommand.Fill(dslogin, "Login")
If dslogin.Tables("Login").Rows.Count = 0 Then
Response.Write(dslogin.Tables("Login").Rows.Count = 0)
Label3.Text = "Username and Password Not Found.Please Try Again!"
Session("UserID") = dslogin.Tables("Login").Rows(0).Item("UserID")
Session("Username") = TextBox1.Text
End If
End Sub

i m getting : output as:

Username and Password Not Found.Please Try Again!"
instead i have that username in the database. Also i m inputting correct Username and Password.

Sorry i m new to ASP.NET so could u explain what is CODE tags.
If it is possible for u can u modify the code i have posted such that it works correctly.
Thanks for Replying me.

The forum software uses code tags for posting code. They are clearly explained in the message editor when you post a message. Just follow the instructions. Also, we use full complete standard English here, instead of the substitutions such as "i"and "u".

I don't code in VB.NET sorry. In any case, ASP.NET Authentication is a well-covered topic with thousands of tutorials on the topic available on the web. Glancing over your code, I see no obvious errors. I tend not to use DataAdapters and DataTables and all that mess. I use stored procedures. You execute them, get the response into a simple DataReader, and do what you need to do.