VS 2008 - Securing ASPX Web Server

I do have before a web server w/c is aspx. its like an online game panel w/c players do shop via web. but suddenly 1 day I was "SQL INJECT" i don't know what they do that the injected me.how do I secure my pages this is what i only use to all my pages to prevent entering characters such as " ',%,!,@,#,$,%,^,&,*,(,),.," all special characters will not be allowed. are there any else in order to secure it.?

Code:
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
Label2.Visible = False
Dim userCleared As New System.Text.StringBuilder
Dim QuestionCleared As New System.Text.StringBuilder
Dim AnswerCleared As New System.Text.StringBuilder

[code]....

and how do I secure to the Direct browser thing? when i checked the IIS7 logs. i saw one IP w/c went to the /Webresource.axd iidjjfme9393j 4m9 mdmf9 um45d m89fm8jhvrm9u9mu30306bm0n.

some like encryption i don't what is this.