Slackware 13.33, Linux 2.6, NVidia 6200, XFCE4,
SDL 1.2.

Discovered that some SDL games display only black screens when switching to some video mode or window.
These are programs that I used extensively before.
One game will hang XWin when trying to back out of it. It continues to run, logging execution time, while it is hung. I have to sigkill the game from another console, where upon it takes down XWin in a crash.

When one game is started in Window mode (no change of screen video mode) sometimes it shows the graphics, and sometimes it is a black window.
In these cases I can get to the console to kill the process.

The other game will back out (ESC key) from the black screen and will shutdown normally.

I have been trying to figure out what happened.
This is the recent history.

1. Installed some themes, mostly to help with a GTK+ problem. Most of them required Murrine, which Slackware does not have, so I isolated them in a separate directory. Maybe I will be able to get Murrine, or maybe not.
Maybe it has left some Murrine specific settings around in my settings ??

2. Changed the XFCE window theme to xfce-dusk.
Have changed it back again now, but no fix.

3. Changed appearance theme to Raleigh, some others, and then back to Alternate.

4. Added a line to /etc/profile.d/gt4.sh to help
gtk find its styles, to stop message
about GTK+ cannot find style. Commenting this line out again has not fixed the problem.

5. Worked on CRT monitor to fix distortion problem.

6. Have compiled, installed the Glest game and played it a few times. It runs and quits normally.
It uses GL.

I am going to start the tedious process of single stepping through a debug version of the one game.
I have already verified that it hangs the process in the game loop instead of cleanly crashing, this will not reveal the problem exactly.

Any one have any ideas or other experience that would help?

It was suspicious that this trouble showed up right after messing with the themes.
There is a combination of causes, none of which has been the themes.

The monitor has selectively failed only for 800x600 mode. The 1600x1200, and other modes still work. To fix the distortion problem I need a 11 Amp, 400V, FET, that costs $1.50.
That will probably bring back 800x600 mode, but I don't why.

Backdoor changing the default of the one game to 640x400 has made it usable.
It has another problem that is causing a hang, and I don't know more yet. That is why it sometimes fails to display in a window.

Why killing the hung game also kills XWin, I don't know.
XWin should not crash that easily.