Faulty iMac - screen 'roller blind effect' then lock up :-(

[PedroDiniz]

Hi,

My Dad is having some problems with his iMac. Specs as below:


Model Name: iMac
Model Identifier: iMac6,1
Processor Name: Intel Core 2 Duo
Processor Speed: 2.16 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache (per processor): 4 MB
Memory: 1 GB
Bus Speed: 667 MHz
Boot ROM Version: IM61.0093.B07
SMC Version: 1.10f2
Serial Number: W863702QVGN

NVIDIA GeForce 7300 GT:

Chipset Model: NVIDIA GeForce 7300 GT
Type: Display
Bus: PCIe
PCIe Lane Width: x16
VRAM (Total): 128 MB
Vendor: NVIDIA (0x10de)
Device ID: 0x0395
Revision ID: 0x00a1
ROM Revision: 3021
Displays:
iMac:
Display Type: LCD
Resolution: 1920 x 1200
Depth: 32-bit Color
Built-In: Yes
Core Image: Hardware Accelerated
Main Display: Yes
Mirror: Off
Online: Yes
Quartz Extreme: Supported
Display Connector:
Status: No display connected

When he is using the internet he is experiencing some bizarre things!
The screen begins to get dark, starting at the top of the screen and moving down the screen like a roller blind, until the whole screen has darkened - you can still see the desktop image underneath - its a bit like when you select the Dashboard, only darker. Then a message pops up, much brighter than the darkened background. The message says,

"You need to restart your computer. Hold down the power button for several seconds or press the Restart button"

The rest of the message box is obscured by what I would describe as colourful TV interference. Like an untuned TV picture.

If left, the iMac goes to sleep, but won't awaken. It just locks up. The usual sleep LED on the front of the mac, which usually blinks, is not lit up at all.

I've attached a screen shot to show what I mean. The actual screen is darker than it looks in this image - I think the flash has caused it to look brighter here, but hopefully you get the idea! Cheers.

Any ideas VERY welcome please!!

Thanks in anticipation.


PS: apparently this doesn't happen at all if my Dad is not using the internet at the time, and it also started after he had posted up a message on a boat classified ad website.

 

[Jethryn Freyman]

That's called a kernel panic. Could be a hardware issue, run the Apple Hardware Test.

 

[Makosuke]

Normally kernel panics (hard crashes--Mac equivalent of a bluescreen or the old-school bomb) are caused by either an external hardware conflict (bad USB device or something), bad low-level software (a driver or system hack you installed), a corrupt MacOS install (rare but possible), or a physical problem with the Mac's hardware.

The fact that the panic message is garbled makes me think it's one of the last two; something's chewing it up before display, making me think it's either a hardware problem or corrupt OS install. Running the hardware test disc that came with the computer, as Jethryn Freyman suggested, will hopefully tell you if it's a hardware problem. If that comes up clean and you haven't installed any low-ish level software (like a hack or driver) then try unhooking anything not vital to using the Mac. If it still reoccurs, then try an OS "archive and install"--time consuming, but will probably fix it.

 

[BlueRevolution]

Yeah, I've never seen the kernel panic message look garbled like that...

 

[PedroDiniz]

Thanks!

Hey, thanks for all the advice I'll call my Dad tomorrow and let him know what you folk suggest and let you know how I get on.

Thanks again, much appreciated!