A couple of weeks ago I upgraded the laptop I use at work to Jaunty, and since then I couldn’t get the external monitor to work properly.
This laptop has two graphic cards: an Intel one integrated on the mainboard, which uses few battery power; and an ATI one with all the bells and whistles, which of course takes more battery. On Windows the graphic driver can change from one to the other on the fly, but on Linux you can’t. You need to go to the BIOS and select one, disabling the other one.
So since I upgraded to Ubuntu 9.04, I the Intel card (which is the one I always use, I use this laptop for work only so I’d rather have half an hour of extra battery than ultra-fast OpenGL… heck, I even have compiz disabled) wouldn’t even boot, X hanged while booting when using that card. And with the ATI card and the fglrx driver, getting the external monitor to work is a PITA. And I need it, as from time to time I give presentations and training sessions and need to hook the laptop to a projector.
I finally found the solution on a Ubuntu forum somewhere (lost the link, sorry): uninstall the fglrx driver! Even if I didn’t use it, even if the ATI card was disabled on the BIOS (wouldn’t even show on lspci) and on the xorg.conf file was using the Intel driver and not the fglrx one, if this driver was installed X would crash when using the Intel card. Uninstall it and voila! The Intel card works again and so does the external monitor configuration applet. Weird.