The latest Ubuntu update broke X.  I don't know if there's a fix out just yet, but the defect, and fix, is referenced here:
http://www.ubuntu.com/FixForUpgradeIssue

Craig Brooksby wrote:
> The westside meeting on Tuesday (covering Joomla!) was very good.  You
> got to show up in order to experience it.
> 
> The latest Ubuntu update resulted in it not playing nice with my
> cheapo video card.  It fails to enter the desktop, and falls into the
> command-line level.  I have been over and over the x-configuration
> stuff -- can't figure it out.  Stuck.
> 
> My mobo requires a PCI-E video card -- no support for AGP.  THe cards
> were too expensive (last year) so I found a cheap PCI video card.
> (yes, plain old PCI),  Worked great (if slow) until a few days ago.
> 
> I am thinking of shopping for a PCI-E card now.  I went out to the FSF
> site, but there is little detail there.
> 
> Anyone have any practical advice on selecting an inexpensive,
> linux-compatible PCI-E video card?
> 
> Thanks --
> 
> Craig
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