Vista - Logoff/on Black Screen

Good afternoon. I am experiencing a problem with Vista on two same model Dell Precision M4400 laptops. If I login to our domain and then logoff and remove the LAN line to login locally - basically all I get is a black screen - never goes into Vista at all and I have to shut the machine off. If I use the switch user feature - that seems to work ok. I was curious if anyone has run into this problem before.

Thanks!

More detail would help.

How far into the second boot does the machine get? Can you see it POST? What about the "Microsoft Corporation" logo while Vista is booting - do you see that?

Do you see this issue if you shut down and then boot-from-cold, or does it only manifest itself when attempting to "restart"?

What about if the second boot is into safe mode? (Assuming you actually get so far as to have the ability to choose - press F8 during startup)

Basically, if I'm logged in to Vista - at first connected to your network then if I logoff the domain and try to login locally I get a blackscreen. If I wait it out - 15 mins or so - Vista finally comes up.

If I reboot - all is fine, just when I use the "logoff" and then log back in. It makes me wonder if it's a profile type issue? I had found a suggestion to shut off the Nvidia Display Driver Service - which I did. At first it seemed to help - but now I"m back at the blackscreen for 15 mins before getting into the desktop if I used the logoff option. If I used the "switch user" option - I dont have the same experience.