The computer freezes on 10.6.3 and later

10-11  Source: Network gathering  Views:0 

I got a freezing / crashing problem on my iMac. It comes in three variants:
1. At some random moment (that means regardless which apps are open, sometimes even just after starting up*) the screen goes black, as when going to sleep. If there is anything happening on the computer (i.e. a YouTube video playing, or music in iTunes), it will continue, only with the video turned off. Sometimes ( I don't know what it's related to) if I press the power button for a short while - as when I make the mac go to sleep - the screen "wakes up", and everything works well again. Sometimes this doesn't work and a shutdown-restart is required.
2. At some random moment the screen would freeze - without going black - and the computer wouldn't respond, the only solution being a shutdown -restart using the power button. When this appears is as I said, random, but lately this sort of malfunction happened to me when I was trying to open an app (Mail or Chrome) from the dock...
3. The same as in 2., but if I wait for a minute or so, the freeze ends and the computer goes back to normal.
When these things happen, I get no error message or log, like with kernel panics, so I guess this is not a panic thing...
I have an USB hub (detached it now, to see if it changes anything) and a Wacom Intuos 4 tablet attached to my computer. I found a thread on these forums regarding Intego VirusBarrier causing crashes, so I uninstalled it and removed it altogether - without any notable changes.
I tried resetting the PRAM - it semed to solve the problem for several days, but then it happened again.
I updated the system - via Software Update, first to 10.6.4, then 10.6.5 - the freezes seem to happen not as often as with 10.6.3, but they still happen.
I repaired the permissions - nothing changed...
Could anyone help me with this? These freezes are not only annoying, they also cause me to lose whatever work I was doing...
Thanks in advance,
* I have quite a lot of software on my mac, so I'm not sure which could be possibly causing trouble... The ones that are open most of the time - and also are opened at login (since some of these freezes happened to me right after logging in, one of these could be the culprit) are:
The Hit List
Adobe updater
VMare Fusion Helper
A CD is stuck inside and refuses to be ejected - some mechanical issue, not a software one (I can hear the CD making noises as if it were coming out of the drive, but then something stops it and it returns back to its original position).
Post in the Intel iMac forum area regarding your issue -
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