Troubleshooting 10.7.2 Intermittent System Stalls and Freezes

Question

Context
Problem is occurring on a PowerMac 2.66 GHz Dual Core Intel Xeon running OS 10.7.2 with 6 GB RAM.
4 Hard drives installed. Normal startup drive is a 600 GB Western Digital VelociRaptor 3.5" drive. Other drives are Western Digital Caviar Black and Caviar Green drives.
No airport or bluetooth cards installed.
Internet access through ethernet connection to Netgear Gigabit Wireless router.
30 inch Cinema Display, wired mouse and keyboard.
Problem Description
For sometime I have been experiencing intermittent system stalls and freezes. None of my troubleshooting has identified the problem. Sometimes when I am doing something, the system will freeze for a few seconds. There is no spinning ball. I am able to move the cursor but it retains the shape it was for the document I was working in but I can neither shift to another application nor shift to another command with the application I am in. Sometimes this behavior will end and normal operation resume. Or it will continue into a system freeze. The system freezes are such that only a power down will work. Sometimes they occur when the computer is asleep and sometimes when I am actively using it. This morning I did receive a spinning ball but it disappeared but the stall continued until, after a minute, I treated it as a freeze since nothing worked except the ability to move the cursor around the screen.
When I became aware of this behavior, it was after I had incrementally upgraded to OS 10.7.2. I later used the Mac OS 10.7.2 version 1.1 combo update. The problem continued.
Troubleshooting
I have been systematically reviewing the console log to identify messages that might identify problems. For example, I located and removed a couple of files in the Library/StartupItems, Library/LaunchAgents, and Library/LaunchDaemons folders that were associated with applications already removed. I have also dropped several apps from my automatic launch sequence.
I have used several utilities to test RAM and other hardware and all tests have passed.
I have switched drives to startup and while I did not stay on a drive using 10.6.8 long enough to experience a system freeze, I did experience a system stall lasting for several seconds. Therefore I do not think it is a drive problem.
I have reduced to minimum the software being used and system has lots of free memory. Memory tests are good. (In Single User mode ran memtest for 2 runs.) Memory problem is unlikely.
=> Reviewing console messages, I find no correlation between the freezes and what is recorded in the logs.
Any suggestions as to how to proceed at this point?

Answer 1

The problem has been solved. In addition to the bad DIMMs, I had a defective video card and there were some software problems. The defective card was replaced and ran well for over 24 hours under intense computing tasks without problems using a Technican personailty. When I used it, I had problems right away. In consultation with Apple, I made the decision to erase (after cloning everything) and do a clean installation of Lion and all of my software. I have not completed installing everything but I have those tools I use on a daily basis now available.
Some Lessons Learned
If you are doing something like this, do not use Migration Assistant to speed up the process. It will bring in everything and you will not really have a clean install.
It is easier if you make the Library on your new Lion drive visible and make the one on your old clone visible too. To avoid permission problems, you need to copy files into a Shared User folder and then copy them into the new destination folder.
If you don't do it right and you find you have problems, check out this link on how to repair User Permissions in Mac OS Lion: http://osxdaily.com/2011/11/15/repair-user-permissions-in-mac-os-x-lion/