A large Slackware update came down the pipeline on my work desktop this morning. One major change in it was that the Xorg server had been upgraded significantly. I found this out after rebooting and then typing startx to fire up X Windows. The screen went black, it switched to graphical mode, and then I got an unmoving underline symbol at top left and that was it. It was locked up hard. Ctrl-Alt-Backspace did nothing.
I had to power the computer down and then restart it. I tried a few things but they all resulted in the same lockup. I needed to get some work done, so I opted for a brutal solution. The /var/log/X logs indicated that it was trying to load device drivers for mouse or keyboard and they were missing so it was locking up. I was fairly sure that my xorg.conf was wrong. It pre-dated the new Xorg server, so was probably the culprit. I renamed the xorg.conf file, and started X without one. And it worked. I was able to get X up, open my windows and get to work.
Except it looked awful. Images were low quality, fonts were thin and reedy. It was ugly. Probably low depth and default fonts. In the afternoon, I had some spare time so I revisited the problem.
I ran xorgsetup, answered a few questions, and created a new xorg.conf. I edited it by setting the horizontal and vertical refresh rates for the monitor, and then the modes for the display. I have one very large ViewSonic monitor that is basically a television set. It needs special sizes and settings. Once I added that data to xorg.conf, I restarted X and it was all beautiful again.
These things keep me on my toes and keep my troubleshooting skills honed.