I have Debian on two hard disks. Both independently running Debian, firefox, no Desktop environment.

For no obvious reason (not sure, but perhaps a JaVA database was in process of saving) the X server shut down for user. I found that user could no longer start X, but root had no problem.

Because running as root interfers with my work, I booted to another hard disk and started X as user with it. I got a half day's work in. However, after a while (as the JAVA database was saving) I lost the Xserver on this system as well, although again could run it as root.

I tried removing user's .Xauthority file and rebooting, but no luck.

I assume the hang of the JAVA application was the result of X shutting down, not its cause. It the
app was in process of saving on both hard disks, that may be a coincidence because I'm nornally using that database.

In first log file there is no error. On second system, at end of log file:

(EE) Failed to load module "nv" (module does not exist, 0)

(EE) Server terminated successfully (0). Closing log file.

None of my partitions are filled. I do not have /etc/X11/xorg.conf files.

Have you checked /var/log/Xorg.0.log or /var/log/messages (or the SystemD logs) for any hints as to why X is having issues? (Those files are present on my Debian 8.x system.)

Someone suggested I check Xorg and messages logs, but my original query indicated that there was nothing unusual in the logs.

I created a "test" account, and had no problem having it startx. So I want back to remove and recreate my user account. This
did not resolve the problem. I'mystified. How can I creast a "test" account that works and a restored user account that does
not? Is it possible that the ampersand in my account PW might cause a problem?

The problem is solved to some degree. In .fetchmail/startup I execute a customized emacs session
to run a file named "chars":

exec emacs-util ~/cribs/chars.

The script emacs-util has the lines:

emacs -q -l /home/haines/.emacs.d/elisp/emacs-util &
exit 0

The command $ emacs-util opens an emacs session. If I try $ emacs-util /home/haines/cribs/chars,
the file does not load.