System: Intel DG965WH motherboard (G965 chipset includes onboard video)
Monitor: Sony CPD-G400
OS: FC6

Fedora Core 6 uses the i810 driver for this, and it has had trouble
setting the sync frequencies correctly since day 1. It has been
mostly stable until the latest set of FC6 patches.

The Xorg log file contains some warnings that might be germane.
Here's a selection. The entire file is viewable at
http://www.jhmg.net/misc/X/Xorg.0.log

[snip]
(--) Chipset 965G found
[snip]
(WW) I810(0): Extended BIOS function 0x5f64 not supported.
[snip]
(WW) I810(0): Extended BIOS function 0x5f05 not supported.
[snip]
(II) I810(0): Will use BIOS call 0x5f05 to set refresh rates for CRTs.
[snip]
(WW) I810(0): Extended BIOS function 0x5f05 not supported.
(II) I810(0): BIOS call 0x5f05 not supported, setting refresh with VBE 3
method.
(II) I810(0): Setting refresh with VBE 3 method.

The end result is wildly wrong horizontal/vertical sync, resulting
in either a totally white screen or severe distortion. I've tried
letting Xorg do its own runtime config (move aside /etc/X11/xorg.conf)
and also generating a new config with "Xorg -configure", with no
luck.

Can someone suggest a course of action to troubleshoot this?