Hello Karen,
I have seen this same issue - generally after I had plugged an external monitor into my laptop  and used dual-display.  In my case, the login applet was there, but invisible - and I found this out by happenstance when I clicked where I thought the window would and typed out my password and the system let me in.  Now that you reminded me of this issue, I can not recall how long ago it had stopped occuring.  I would have been on RHEL 6, however.

You can certainly attempt to "re-install" the packages using yum

# yum reinstall <pkg>

However, I don't know if there is  reinstall option for an entire group.

Also, this is a question for the group:  Is 'startx' the correct way to start GDM on RHEL 5, or RHEL 6 for that matter?  It's been a long time since I have had to deal with desktop issues.

Hello again,

While researching a response for you, I realize I am really out of my element with desktops :-(  And unfortunately I do not have a GUI-enabled system to play with at the moment.  I will spin one up later today and dig into this.  In my experience I would not execute a single command (such as gdm or startx), instead if I was playing around I would use init to change runlevels to start the display manager.  I.e. when using the Nvidia display driver, it has to be installed when the Display Manager is not running.

-- Update /etc/inittab as follows

id:3:initdefault:

I modify the inittab instead of simply using grub in case I run into issues, etc... and I end up rebooting again in the middle of the process.

# shutdown now -r

-- Then

# init 5

-- Validate that the display manager and video drivers work correctly, and update /etc/inittab again

id:5:initdefault:

Karen,

Along with above suggestions, also if you need a gnome desktop run a command below to install GNOME Desktop Environment.
# yum groupinstall "GNOME Desktop Environment" -y

Then start X Window System.

  # startx

I assume that you have already edited inittab file to run system on runlevel 5.

Regards,
Anand

Also - you have identified a very good use case for a RHN Satellite installation on-site ;-)  You could have a completely disconnected environment and still take advantage of the power of RHN.  You can private message me if this is of interest and I can provide more information or help you find the right resource at Red Hat to provide info.  If you have not worked with Satellite, I highly recommend you (and your team) see a demo.  It's good stuff!

Hey Karen - I'm actually not sure how to PM using the groups.  Henry/David - is this possible?  

I also figured it may be a undesirable practice to publish contact info here in the forums.

Does your team currently have a Red Hat rep?  If not, let us know what geographic region you are located in and I'm sure someone from Red Hat can step in and help get you in contact with them.

Let's wait to hear what the forum mod's recommend to move forward.  I am really excited for you to hear/see what Satellite (in a disconnected environment) is capable of doing for you.

Take care

I have used the reinstall option for various reasons (sometimes as trivial as not creating a backup of a configuration and accidentally messing the file up).

Now, to answer the other part of your question: I have had 100% success using reinstall, which is not to say that I will continue to have absolute success, but... it has always worked for me ;-)  The only potential issue I can anticipate is the reinstall may overwrite an existing config file, but I believe it would make a backup of that file (depending on the procedures yum will use).