I'm experiencing frequent temporary hangs during which my computer seems to continue operating but the display is frozen. I also occasionally get a corrupted screen with lots of small horizontal bars spread across it. These seem to be associated with the temporary hangs: if the screen is corrupted then it's usually hung as well. The corruption will then start moving like the scan lines on an old TV or as if data was being illegally written into a graphics buffer. I would have diagnosed a hardware problem, but it doesn't occur when I've booted into safemode. Sometimes the screen is totally stuck and I have to do a power-button reboot. It doesn't always come up normally, unless I'm booting into safemode.

In an attempt to solve the problem I've opened a new user account. The problem still occurs, unless I'm in safe mode. I've run applejack. Still occurs. OnyX. Still occurs. I've removed everything from the login items (via System Preferences / Accounts - is there anything that goes deeper?) Still occurs. Any other options? I'm willing to try reinstalling, but the other problem I have is that I get told that I can't install Mac OS X onto this volume.

Here's a sample of the terminal messages I get during the hangs:
ystem hangs:
11/01/09 2:21:59 PM kernel NVDA(OpenGL): Channel exception! status = 0xffff info32 = 0x8 = Fifo: Watchdog Timeout Error
11/01/09 2:21:59 PM kernel 0000000c
11/01/09 2:21:59 PM kernel 00100000 00000000 00000000 00000040
11/01/09 2:21:59 PM kernel 00000000 00000104 00000000 00000020
11/01/09 2:21:59 PM kernel 00000000 00000000 00070003
11/01/09 2:42:06 PM kernel NVChannel(OpenGL): Graphics channel timeout!
11/01/09 2:42:18 PM kernel NVDA(OpenGL): Channel exception! status = 0xffff info32 = 0x7 = Fifo: PTE Error
11/01/09 2:42:18 PM kernel 0000000b
11/01/09 2:42:18 PM kernel 0000000b
11/01/09 2:42:18 PM kernel 0000000b
11/01/09 2:42:18 PM kernel 0000000b
11/01/09 2:42:18 PM kernel 0000000c
11/01/09 2:42:18 PM kernel 00000100 00004097 0001b8d5 00000000
11/01/09 2:42:18 PM kernel 00028218 00000b4c 00000000 00000002
11/01/09 2:42:18 PM kernel 00000000 00000000 00000000
11/01/09 2:42:18 PM kernel NVDA(OpenGL): Channel exception! status = 0xffff info32 = 0x7 = Fifo: PTE Error
11/01/09 2:42:18 PM kernel 0000000b
11/01/09 2:42:18 PM kernel NVDA(OpenGL): Channel exception! status = 0xffff info32 = 0x7 = Fifo: PTE Error
11/01/09 2:42:18 PM kernel 0000000b

Since this occurs on both accounts the problem is related to something in the system area. Add to that a safe boot...

1. loads only required kernel extensions (some of the items in System/Library/Extensions).
2. disables all fonts other than those in /System/Library/Fonts
3. It moves to the Trash all font caches normally stored in /Library/Caches/com.apple.ATS/(uid)/ , where (uid) is a user ID number such as 501.
4. disables all startup items and any Login Items.

That would appear to limit the likely culprit to...

• a corrupted kernel extension (item 1),
• a corrupted font (FontBook can check for font corruption)
• something in /Library/StartupItems, /Library/Input Managers, /Library/Contextual Menu Items, /Library/LaunchAgents, or /Library/LaunchDaemons.

Sorry I can't be more specific.

Further to joemike's response:

> I would have diagnosed a hardware problem, but it doesn't occur when I've booted into safemode.

I have a recollection of a VRAM issue that didn't occur during a Safe Boot, so it might pay you to run your Apple Hardware Test disc a coupl'a times.

> I'm willing to try reinstalling, but the other problem I have is that I get told that I can't install Mac OS X onto this volume.

Without specifics I can't be certain, but your error message generally comes up when your installation is of a later version of OS X than is your restore disc; in such a case you must click on "Options" and opt for an Archive & Install. (Be certain to check the "Preserve User and Network Settings" box if such is your intention and to back up any data you can't afford to lose.)

If you go the A & I route you should run "Repair Disk" while booted from your restore disc (at the least) before doing so.

Joe -
I'm having the exact same issue with my Mac Pro. I believe it started with the update to 10.5.6 though I'm not sure. So far I have not found a solution. How about you - did you do an Archive and Install, and did it help?
Cheers,
Ruedi

Ok, I just did an A & I and have the system back up running 10.5.0. The symptoms are still there, worse than ever. Bummer. Hardware diagnosis indicated no failure, though. I guess I'm lost. Feels like I'm back in the Windows world, which I left two years ago.
Ruedi

I would suggest resetting the PRAM where the video settings are stored and take a read of this message board thread incase it gives you some pointers where other users of MacPros have had this trouble, and fixed it but in an earlier version of Leopard.

Read all about it here

dude... G4 MDD 1.42mhz... 10.5.6 is ruining my life. Tried everything... everything except waiting for apple to release 10.5.7 and praying they fix this mess.

I fixed the problem by replacing the video card (An Nvido 7300GT which search engines might also spell Nvidia 7300 GT). My thanks to the user who pointed out that some hardware problems don't manifest during a safe boot: that was the key.

> My thanks to the user who pointed out that some hardware problems don't manifest during a safe boot: that was the key.

Yours is the second bad video card to pass Safe-Boot in 10 days.

Happy to have been helpful.

Ok, turns out mine was a hardware issue as well. I brought the Mac Pro to the shop where they replaced the video card (Nvidia 7400 GT) and all is well now. Took them more than a couple of weeks and cost me some dough as it happened 13 months after purchase. Next time I'll consider extended warranty. Oh well...
Ruedi