I have the exact same problem. Brand new 20" Aluminum iMac running 10.5.1. Reboots randomly no matter if I'm in safe mode, normal mode, when I boot from the install disk, when I'm trying to run Apple Hardware Test. Tech support thought it might be due to brown outs so I took the computer somewhere else (neighbor) and still have the same problems. I have NO idea why this is happening and it's frustrating the crud out of me.
I have the exact same problem. Brand new 20" Aluminum iMac running 10.5.1. Reboots randomly no matter if I'm in safe mode, normal mode, when I boot from the install disk, when I'm trying to run Apple Hardware Test. Tech support thought it might be due to brown outs so I took the computer somewhere else (neighbor) and still have the same problems. I have NO idea why this is happening and it's frustrating the crud out of me.
If that doesn't fix it, there may be a problem with the Power supply and you should contact Apple and make arrangements to take or send it back for a replacement.
Started doing it pretty much right out of the box. I got the computer the day after christmas (boxing day for some). The first time I thought maybe I kicked the power strip or something but no. Nothing has helped yet. I'm waiting for tech support to return from their vacation then I'll follow up with them. I'll keep you posted.;;;;
Yep. SMC reset was the first thing I did on the phone with Tech Support. Didn't help. Opened up disk utility and verified disk permissions. No problems. Attempted to do the extended Apple Hardware Utility test but the computer restarts before it can finish. Same thing for an attempted re-install from the install disks that came with the computer.
I had the same problem with my Intel 20" imac. Got it new and within a couple of days started randomly restarting - I tracked it down to when I was using heavy processor use. Tried everything: PRAM, SMC, turning TM off, turning all power saving off. I finally solved it (touch wood). It looks like it was over heating. I downloaded ISTAT Pro widget all temperature shot up above 50 degree C when encoding a movie so I downloaded fanspeed controller and increased the idle speeds (CPU & HDD) until my temps stablised below 50 degree C.
Spoke too soon! I am still getting random restarts but it definitely more stable than before. It seems to only do it now if I am encoding a movie and also transferring a large file to a USB hard drive both at same time.
I have the same exact problem. I recently got my iMac less than a month ago and it randomly restarts several times per day. Let me know if you figure out what is wrong with yours. It seems many people are having the same problem.
Whilst using Safri my CPU fan stuck on at full speed - hardware test gave an error - no change on SMC reset etc. so I took it back and got a replacement. No issues yet!
This started happening to me AFTER I installed 2GB of RAM. I originally only had 1GB. The crash is most frequent when I'm using a lot of system resources [ie. when I'm converting a movie using VisualHub, and listening to music].
It happens randomly to me too, and after I installed 4gb ram. I found a temperature monitor widget and it looks like it's over 50 degrees, so I will try the method of downloading that program to turn fans on when it does.
little disappointed...4gb ram is a little disappointing too...
My late 2007 iMac randomly restarts, too. I reset PRAM and SMC with no improvement. Suspecting I had bad power supply hardware, I took it to the Apple Store and they tested it hard for 5 days nonstop. It never restarted. I took it home last night and got a random restart this morning.
I have noticed that the restart often happens just a few minutes after I get a "software update available" message and I don't click "install and restart now". But the computer does not shut down apps and log out gracefully, it just suddenly blinks out right in the middle of whatever video or music is playing. And when it comes back online, the software has not been installed, so I really don't know if these things are related. Furthermore, while the computer was in the Apple Store, software update offered an update and I intentionally did not click "install and restart now" just to see if it would restart. It did not.
My current thinking is that if the iMac is okay, then the circuitry in my 65 year old house may be to blame. I know the circuit that the iMac is on is shared by the kitchen downstairs because in the past I've blacked out my office by running the toaster oven. Nothing else in my office is affected when my iMac restarts, but perhaps I'm experiencing minute brownouts on the circuit that only affect the computer... is this possible? I'm thinking of buying an uninterruptible power supply (UPS) to even out the voltage.
The problem is, I had the "auto-restart after power outage" option turned off when I experienced the restart this morning. So I'm not so sure if my house circuitry is the problem. If it were, you would think my computer would have just shut down and not restarted.
Does anyone have their spontaneously restarting iMac hooked up to a UPS? If so, we may rule this possibility out.
Jason
P.S. I have factory installed RAM, no overheating issues, and no peripherals attached other than the keyboard/mouse and a Westell router.