IMac freezing intermittently--every few minutes. How can I fix this? A couple of days ago, I was browsing, and downloading something from Usenet, when my iMac all of a sudden froze up, grinding to an unbearable slowness.  After trying to tolerate what was happening for 5 minutes, hoping it would pass, I finally gave up, and restarted the computer manually.  To my horror, for about a day, I was plagued with the interminable locked up gray Apple startup screen, but thankfully the next morning, left it on from a  restart to find later that the computer had managed to boot up to a login screen, everything seemingly fixed.

That was background.  Now I have a different problem: My iMac is subjecting me to intermittent freezing episodes; I will be writing, or browsing in peace for a few minutes, before everything locks up, save for perhaps only the cursor.   When the hanging is finished, the computer then resumes the missed operations (typing, etc.) in a hurry, as if one were watching a fast-forwarded video.   Each hanging episode lasts from anywhere from 5 seconds to upwards of a minute; moreover, the system pops a window telling me that I don't have enough disk space for memory, though Finder consistently tells me I have upwards of 30GB worth of space (on a 250 GB HD).   There's also another curiosity: When I tried using Software Update to update everything &mdash; trying to fix this problem &mdash; upon Restart it told it couldn't install a recent Security Update because "the source media [you?] are installing from is damaged."

What's my causing my problems? How can I fix them? Unlike a previous related question, I don't think this has anything to do with Youtube or my browser; closing near every window, including Chrome, has no solved the problem, or mitigated it in any way.   I was also wondering could it perhaps do with something I downloaded -- could Trojans somehow associated with the movie I was downloading have anything to do with this problem?  I'd really appreciate some help on this; this freezing has rendered a significant part of my workflow virtually unusable, and I don't consider myself very computer savvy.
It's very unlikely you downloaded something or broke everything with one download. Also - with at least 4 things not working well - please protect your pictures, emails just in case it's a hardware failure.

When only one thing is broken - it's often worthwhile to poke, learn, understand what broke and look for a fix of that one issue.

For any group of three or more problems, there's one solution that always works (and often saves a lot of time):


Back up anything you can't afford to loose and get someone who is a bit tech savvy to verify you have a workable backup that you can restore if needed.
Erase the mac and install just a clean system from the media that came with the mac. 


This will quickly let you know if the hardware has failed. It will also solve nearly all software issues. Once you have surfed the web, made sure it is reliable, then you can run updates, restore your personal files and get on knowing it was just some corruption of the software.

Don't feel bad getting help from someone (even paid) if your savvy is for things other than a computer. A good tech can erase and install Mac OS X in 10 to 30 minutes. A good tech might take 4 hours to 4 days to pick apart all the things that could be wrong and tell you what happened. With multiple issues, it's hard to tell what was the root cause and what was just a subsequent failure.

It's often so much easier and efficient to just clean up the mess, start fresh, and keep an eye for any sign of the problems recurring. You will then have better data on the problem. You will also have a backup of your important files.

Since your computer can't tell if it has enough memory to run, (or is truly out of space) you can't really trust itself to fix itself which is why I jumped right to backup / restore for anyone on a situation as you describe. Also, if you were to determine exactly what broke, and did the fixes right, if it freezes or doesn't complete your fix - you will still be in the same badly working situation.

Best of luck - some good people have made answers with great advice here as to what could be wrong. I wanted to weigh in with a different sort of advice since no-one (you included) had mentioned protecting your data files.