iMac 27" i5 Freezing - Mouse still active, no video distortion, help!

Hey guys I really need some expert help here with my i5 27" iMac. Full system specs at bottom. It should be noted that the only after-market hardware I've added was the 4GB of RAM, upgrading it to 8GB.

The system will periodically freeze, ALWAYS when I'm doing fairly resource intensive tasks. The most common scenario is I will have a game running with Safari or Chrome, iTunes, Notes, and Mail open. The freeze always occurs as I'm switching windows or, just as often, as I'm clicking an icon on the dock. The screen becomes perfectly frozen in time without any distortions or pixellations; the mouse is still active but that is the extent (I can move the cursor but cannot interact in any way). Manual restart is only solution. In EVERY case the system is very hot, I don't know if that has anything to do with it.

Could these freezes be from bad memory in the 4GB I added that is only getting utilized in resource intensive tasks? I ran a Hardware Test using the bootup disk and all things checked out. I bought the Apple Care but I'd really rather wait on that, they are painfully slow with repairs.

iMac i5 2.66 GHz 27"
8 GB 1067 MHz DDR3
ATI Radeon HD4850 512 MB

Freezes such as those you're experiencing are usually hardware related. Two possible hardware faults come to mind:

1. The GPU. Graphics processor overheating (fan problems) will cause freezing and may even show up as distortion on the screen. Doesn't sound like that's what's happening to your machine - but a possibility.

2. Memory. Bad or intermittent memory can cause freezing and or random reboots. This sounds more like what's happening to your machine as it comes under heavy loading (more memory being tasked).

I would remove the additional 4 GB of memory you added and go back to the factory configuration as a test. Let's see if the freezing stops. If it continues, make an appointment with the genius bar at your local Apple store.

Regards.

Thanks, yeah memory is what I was thinking as well. I believe I bought it from Fry's Electronics which doesn't always have the best hardware.

I'll remove the additional 4GB and let you know what I find.

Screen freeze

I have a similar problem and would appreciate advice on how to solve - and I am not a computer expert.

My MAC has OSX version 10.6.4 (big screen). It freezes up just about every day, particularly after a log on. (Presently, the MAC is set up so that any of three users or a guest can log on, if that makes a difference. Only one person at a time uses the computer since it is not networked). Usually it freezes up shortly after log on, independent of user, and none of the force quit functions will break it loose. Have to turn off the system and turn it back on again. Almost always, after turning it back on, it works fine through log out. I have not changed any of the factory settings. No idea of cause or how to fix.