Comment # 3 on bug 934731 from Guido Berhoerster

(In reply to David Westfall from comment #2)
> Sorry screens are :0.0 and :0.1 not :0.0 and :1.0.

OK, that's a big difference. Multi-screen is also a non-standard setup for
multiple monitors so can you please explain the following in more detail:
how is your X server is configured? Please attach your xorg.conf or any
customizations in  /etc/X11/xorg.conf.d/ as well as /var/log/Xorg.*.log so we
can look for X errors.
how do you start applications usually? Do you have a Xfce panel on each screen?
Do you use xfdesktop? Please also attach ~/.xsession-errors-:* so we can see
any application error messages.

(In reply to David Westfall from comment #0)
> After a reboot this morning I am no longer able to use the right hand
> monitor on my system.  My system is configured for multi monitor setup Left
> is :0.0 and right is :1.0.  When I click on the right hand screen, left or
> right, both screens blink and nothing on the right opens up.  Sometimes it

Does your left screen still work, i.e. display the desktop as normal?
What should the right screen display and what does it actually display?
What do you click and what menu do you expect to open up?
What does "blinking" mean, is there a window popping up and immediately closing
again, something else?

> The updates on the 2nd had Nvidia but there was a reboot so I should have
> had the problem last week if this is caused by Nvidia.  The problem did not
> start until this morning.

In order to exclude the nvidia driver update as the source of the problem you
could try switching to the nouveau driver and see if the problem persists.