I have several Active Directory Users and Groups which I want to use for
log in and access restrictions within WSS, which is newly installed on a
Windows 2008 Standard Server.

The WSS is up and running and I am able to log in with the primary
Administrator or any account I have added to the Site Administrators
group. Some other accounts are able to log in too.

Now I wanted to define, that a special AD group has access to the
Homepage (and other WSS sites), so I added the group to either owners of
  Homepage or readers of Homepage, which both does not help, members of
this group still get Access Denied for this page after logging in. I
can't even find some of the AD accounts for adding them manually to the
User groups- although these accounts are visible in AD Users and
Computers and can log in to the computers normally and so on I can't
find them in WSS- AND- THIS will happen to any NEW user I add to AD.

SO it seems to me something about the connection between WSS and AD has
been lost so that it can't find the groups users are belonging to or
can't find some users in general.

What I did after installing WSS was moving the Database to another Disk
as described in a Microsoft Technet article.

What I did too was adding an alternate access connection for accessing
the Page through our Reverse Proxy Server via HTTPS from the Internet.

The login Problem is occuring using the reverse proxy or the standard
access connection to the WSS on the local machine, no matter.

The Server has the newest Updates, WSS has SP2 and is running on MS
internal Database.

Windows Server 2008 Standard w/o Hyper V x64, WSS 3 SP2, Intel Xeon Quad
Core Processor and 14GB of Memory.

I have tried re installing WSS today. I am still missing the same users
from Active Directory in the "add group/user" dialog. I can't figure out
a relation between the users missing but that these are the newest ones
in Active Directory.