Sudden iMac 27 Screen and Processing Issues

I have a late 2009 iMac 27 that I bought used a few months. It was immaculate and had the drive wiped and the latest OSX (10.8.5)installed (and worked great until recently).

On start up (which is slower than normal) the screen will show little repeating windows across the screen and drop down screens will be muddled (see attached photo). It also seems to really bog down on basic tasks like opening the Launchpad which can take up to a minute. When I start it in Safe Mode, the graphics are much better (but not perfect) and processing speed is improved but still slow. Eventually, it always freezes up and I have to hold the power switch down to shut it off and restart it. Except for MS Office, i have very little software on the machine.

I'm new to Macs and not particulary computer savvy. I suspect a trip to the Genius Bar is in my future but wanted to ask you experts first for any advice you may have to diagnose or resolve the issue. Thanks!

Colin

Welcome to the Mac Forums.

Let's do some testing:

Boot your iMac to recovery. Hold down your command and r keys at the same time when rebooting. Keep holding them down until you see the Apple appear. Once you're in recovery mode, select Utilities, then select Disk Utility. Highlight your Macintosh HD on the left side and then select "verify" on the right side. Let's see what that tells us about the hard drive.

The symptoms you describe could indicate problems with the hard drive or it could be something else. Testing the hard drive is easy so it's best to do that first. Let us know the results.

Thank you so much for your help. I followed your directions and got the message "The volume Macintosh appears to be OK", so I guess it's not a hard drive issue. I also checked the "Mac OS X Base System" and got an OK.

Getting the hard drive tested and out of the way is the first step. Let's try a cleanup and maintenance utility to see if we can speed things up somewhat. The only utility we recommend is OnyX which you can download from here. (It's free.) Download the version for your operating system (Mountain Lion 10.8.5) and run it in automatic mode. Read the instructions and follow directions. Let us know if that helps.

Also, how much system memory does your iMac have and how much free space remains on your hard drive?

I downloaded and ran OnyX but there was no improvement. There is definitely a major difference between Safe Mode and standard start-up. In Safe mode, the computer is near normal and with standard start up it's barely functional (and eventually locks up). So does that give a clue on what the problem might be? FYI, less than 50 GB of the 1 TB hard drive is in use. Thanks.

When you start your iMac in Safe Mode, that eliminates all startup programs and removes all third party drivers and the audio. You may have a program or process that's using up an inordinate amount of your CPU or memory when you startup in normal mode.

As a new Mac user it's not always easy to hunt around and track down what's bogging down your machine. Let's see if you can follow this: Start up in normal mode.

Next, go to Applications, Utilities, and open the Activity Monitor application. Click on the tab at the top that says "CPU". Now, take a screen shot of the Activity Monitor window and upload to this thread in your reply. Taking a screen shot is easy.... go to this LINK and follow directions.

Below your reply dialog box you'll see the title "Attach Files" and then below that "Manage Attachments". It's kind of self explanatory. That will give us a chance to see what might be going on with your iMac and why it's running so slow in normal mode. I suspect something is going on in the background that shouldn't be running.

Attached is a photo in lieu of a screen shot (the iMac crashed when I tried to take a screen shot). As you can see, the CPU barely seems to be processing anything. The black lines cover activities that also have 0% CPU usuage. I'll mention a couple of other issues the machine has had in case they are relevant:
-the Blue Tooth module stopped working a couple of months ago forcing us to use a wired keyboard and mouse. I tried every fix suggested in Mac Forums but nothing worked. It may just be that I have to replace the module.
-I notice that when the machine is in sleep mode, I can hear the hard drive spin up for a few seconds every 15 or 20 seconds which doesn't seem right.

Finally, the machine has 8 GB or RAM (neglected to mention in my last post). Again, thank you very much for all your help so far!

Your Activity Monitor is showing zero CPU activity which isn't right. Also, your mention of the the Blue Tooth not working is troublesome. But what seems even more so is the "hunting" of your hard drive when the machine is in sleep mode. I'm beginning to suspect your hard drive again even though it verified. One of the problems with using Disk Utility to verify a hard drive is that it does not verify the electronic or physical workings of the drive. It really only verifies the file and folder structure and whether or not there are bad sectors that have to be locked out.

I think it may be time for you to make an appointment with your local genius bar and have them do a diagnostic. With Xmas approaching in a few days, most Apple stores will be like a madhouse. Might be wise to make the appointment now ahead of time and hope you'll get in there to see a tech shortly after Xmas day. Not an easy job to lug an iMac in to the genius bar. I've been there and done that. Let us know what you decide to do.

Final update: I ended up taking the Mac to the Genius Bar twice. The first time they replaced the Bluetooth module which fixed the Bluetooth but nothing else (cost about $60). Their diagnostic did not show any issues with the video card. However, they replaced the video card (about $200) at the second visit which did fix the problem (finally!). Thanks for your advice and support!

Thanks for posting back and letting us know. I wasn't sure the video card module could be replaced on a 2009 iMac as most iMacs have the video chipset soldered to the logic board. Anyway, I'm glad to hear that resolved the problem and it looks like the labor cost was not too expensive considering how difficult it is to work on an iMac.

chscag said:

Thanks for posting back and letting us know. I wasn't sure the video card module could be replaced on a 2009 iMac as most iMacs have the video chipset soldered to the logic board.

Click to expand...

I was thinking the same thing. "About $200" is certainly a lot less than a whole new logic board...so maybe something must be swappable.

- Nick

p.s. "Curious minds" want to know more...so I looked it up. According to Powerbookmedic.com...there are separate video card parts for "Late 2009" 27" iMac's. Here's an example of one (cost is about $159) so maybe that + labor got the repair total to around $200:

Intel iMac 27" ATI Radeon HD 4850 256MB Video Card

chscag said:

Thanks for posting back and letting us know. I wasn't sure the video card module could be replaced on a 2009 iMac as most iMacs have the video chipset soldered to the logic board. Anyway, I'm glad to hear that resolved the problem and it looks like the labor cost was not too expensive considering how difficult it is to work on an iMac.

Click to expand...

Charley, a member here a while back alerted me that even my late 2007 iMac has a replaceable video card! I checked and it sure does! I would have Bet it did not!

His screen shots to me were screaming video card, especially his Activity monitor one at the very bottom of the AM window.

So Glad Apple fixed it for you.