OK now this may be a long shot but a couple of years back when i first got my dell with vista i had a little problem with the screen where sometimes it would change resolution, sometimes it would not show anything and i had to CTRL ALT DEL and close the screen and it was very annoying.
before anything else i need to say that new drivers fixed my issue (haven't had the issue window Windows 7 Beta).
Please check this website and try the suggestion to disable TMM. http://www.vistax64.com/tutorials/115320-transient-multimon-manager-tmm.html
the procedure is reversible but it may help.
disabling TMM doesn't mean that you CANT use external monitors, it just means that i won't detect them automatically (you'll have to manually press your laptop fn key conbination to get the external monitor).