Not all domains in drop down box

Need to put them back in a workgroup. reboot. put them back in the domain and reboot again.

If you have to do other things in between, like changing the computer name, then reboot after doing that as well.

For some reason, the changes haveto take place in the registry/memory one at a time. If you try to do multiple changes and then reboot, it will not "take."

(begin 'I know you know this' section)
Those domains in the drop down list are placed there by trusts. If domain A trusts domain B, when you logon to a domain A machine, you will see domain Bs name in the drop down.
(end of 'I know you know this'section ;-)

I would check the trust relationships between your domains, and if other machines do see the drop downs (wasn't mentioned in your question) and this one doesn't - there is a trust problem with this machine and the domain. This being said you can use some resource kit programs (NETDOM is the first that comes to mind) to check the trust between the machine/domain or domain/domain. If it is only this machine having issues, I would take it out of the domain, and reboot - verify that there ISN'T a drop down box available (only there when part of a domain). Check AD users / computers to insure the machine is out of the domain. Once that is done, then I would re-add the machine to the domain. If the machine was added to the domain correctly, you should see a new drop down box during logon. The first time coming in you should click on the drop down box and it should take a couple seconds to populate.

Try this, and post a message if it doesn't work ... there are also registry entries you can check, but I don't remember those of the top of my head. I'll post them if you still have issues though.

Good luck.