.NET Active Directory Wrapper    
Access Active Directory From Your C# or VB .Net Code
 

Active Directory
Introduction
Objects
Object Properties

DirectoryServices Namespace
Introduction
DirectoryEntry Class

How to .. in C# .NET
Create User
Disable User
Enable User
Authenticate a User
Change User Password
Get DirectoryEntry of a user
Get Users in a Group
Get Object Property

Other Resources
References

Enabling a user in Active Directory

public static void EnableUserAccount(DirectoryEntry oDE)
{
//we enable the account by resetting all the account options excluding the disable flag
// oDE.Properties["userAccountControl"][0]=DotnetAD.ADAccountOptions.UF_NORMAL_ACCOUNT|DotnetAD.ADAccountOptions.UF_DONT_EXPIRE_PASSWD;
// oDE.CommitChanges();
//
// // oDE.Invoke("accountDisabled",new Object[]{"false"});
// oDE.Close();
object ent = oDE.NativeObject;
Type type = ent.GetType();
type.InvokeMember("AccountDisabled", BindingFlags.SetProperty, null, ent, new object[] { false });
oDE.CommitChanges();
oDE.Close();
oDE.Dispose();
}