This post suggests faulty ATI drivers.
http://www.canmusaogullari.com/2010/08/macbook-pro-with-ati-radeon-x1600-display -anomalies/
I am presently inclined to agree, but there may be other contributors. To date, when my login screen and desktop have the horizontal line problem, it invariably disappears on safe boot. When left for a while, this problem propagates into other windows. I have not been able to verify a temperature relationship. Disabling QuartzExtreme did not reliably help. Deleting all /Library/Internet PlugIns did not resolve the Safari crashing problem. Old plugins may have contributed to the Safari crashing problem leaving other system resources corrupt.
My working hypothesis is that a combination of bad X1600 drivers +/- Safari causes low-level corruption in system resources, which spreads until the system will lockup/freeze. Whatever gets corrupted needs to be fixed to resolve the behaviour. One archive and install crashed and another failed to resolve the problem.
My latest recipe still manages to resolve the login screen and desktop horizontal line problem. (Some parts may prove to be superflous, but I am starting from a position of being able to reliably eradicate the bugs.)
1. restart
2. zap PRAM (hold cmd-opt-P-R when booting until the system chimes a second time)
3. safeboot (hold shift while booting)
4. delete suspected corrupted preferences (move or rename or delete - I think Apple recommends dragging to desktop; I use terminal) - all in /Library/Preferences/System Configuration; .GlobalPreferences.plist; com.apple.windowserver.plist; com.apple.loginwindow.plist
5. delete ATIX drivers as per link above
6. reinstall ATIX drivers by applying most recent OS update (I have been using OS10.5.8 update, since that is what I am using; I also copy the ATIX drivers into another folder in case I need to delete them again - have had to do this once already while experimenting)
7. reboot in single user mode (hold cmd-S while booting)
8. run # applejack AUTO
9. exit applejack before rebooting (press ctrl-C)
10. run # applejack in manual mode
11. manually choose item 3; say yes to clean cache files for specific users; clean your own userid
12. manually choose item 4; say yes to validate prefs for specific users; validate your own userid
13. reboot
Presently, I have QuartzExtreme enabled and am avoiding using Safari to see if the problem will recur. So far so good for a few days. Can anybody who has recurring problems who tries this recipe please report back?
(If you don't have applejack, get it from
http://applejack.sourceforge.net/)