How can i check if user input already exists in database

Hi, im having a a little trouble,
 
I have a page where users can search a database for authors. If the author is in the database it displays info about the author. However if the author doesnt exist it currently errors. I would like to have something that works similiar to the way the CreateuserWizard works to see if a username already exists like the inputted name, But with an author. Im not sure whether there is anything in ASP to accomplish this task already, if anybody knows of anything, could you please let me know.  I dont think data validators will work, so ive tried to make some code from scratch to do the job, im fairly new with asp.  The code im using is below;
Protected Sub BtnAuthor_Click (ByVal sender As Object, By Val e As SystemArgs) Handles BtnAuthor.Click
Dim AuthorString As String
AuthorString = TxBxAuthor.Text
If TxBxAuthor.Text.Trim() = "" OrElse CheckAuthor(TxBxAuthor.Text) ...