getting project to find ajaxcontroltoolkit

I recently had to reformat my computer. 

Then I downloaded Visual Studio 2012 express for web

I had a website where I tried to add nuget, so I could add the ajaxcontroltoolkit, but the only part of the nuget package manager that appears is the console command part.

So I gave up on nuget, and just downloaded ajaxcontroltoolkit to a folder.  Then I added a reference to 'ajaxcontroltoolkit.dll'.  Then I compiled.  I get an error that "Unknown server tag 'ajaxToolkit:ToolkitScriptManager'."

I looked at the code (which used to work) and it looks like this:

<%@ Page Title="" Language="VB" MasterPageFile="~/MasterPageAdmin.master" AutoEventWireup="false"
    CodeFile="editslider.aspx.vb" Inherits="editslider" %><asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server"><%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit.HTMLEditor" TagPrefix="cc1" %><ajaxToolkit:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server"></ajaxToolkit:ToolkitScriptManager>

It is the last line that gives me this error.  Why is this happening?

Thanks

P.S.  I also notice there are ajaxcontroltoolkit files in my bin folder, maybe the duplication is a bad thing?
P.P.S. some other projects on this computer also don't compile.  For instance, I get an error: " 'Linq' is not declared. It may be inaccessible due to its protection level.".  I think I must be using the latest NET framework, because VS2012 was the first program that I downloaded.