It can be a thermal problem that something is not quite right when it is cold but is fine after it warms up.
Make sure all the cables are seated correctly and are clean. ie no oxidation
Ha, that’s a project and a half. You mean the LVDS connector?
I’ll suffer through the problem rather than take this thing apart again, at least until I’ve got more free time. There’s no discernible correlation with thermal either way anyway, but thanks for the input, heat can cause weird issues. Actually, I think I can re-apply heatpads and paste easily enough with just a few screws, so I might do that at some point.
The Temperature widget reads 127 Fahrenheit on the one sensor it detects (so, 53 C). Maybe a bit high but it’s a 2008 athlon. The BIOS on this thing is horribly limited, wish I could set the fan more aggressively. (and it does that **** 0 rpm - full ON/OFF thing that some companies think is just great 
)
There any good fanspeed programs? Probably wouldn’t work with this bios anyway…
As for that troubleshooting Wiki, I get a cnf on glxgears, not the gears or the errors the Wiki expects, and Mesa is installed.