Will reinstall of Snow Leopard help iMac stop freezing?


Will reinstall of Snow Leopard help iMac stop freezing?
I've been having problems with my Mac freezing.  I've tried all kinds of things (verify and repair permissions and disk etc, make sure enough free space, as well as checking fans, disk utility etc) and the problem persists.  It's a 24inch iMac that I bought in late 2008 and the problems have been  ongoing intermittently for  months now.  Basically what will happen is  that I’ll be using it when it will suddenly freeze and the screen goes  blank.  The only thing that works then is to restart by holding down the  power button on the back to turn it off and then on again.  I use it  most often for internet (I use firefox) but the issue has happened when  doing other things too, so I don’t think it’s related to any particular  programme.
I took it into the genius bar and after checking the disks and finding no problem their advice was to reinstall snow leopard.  I was the last appointment of the day before a long weekend and the guy was helpful but fairly rushed.  The thing is that I had this problem with leopard as well before upgrading to snow leopard, so I can't see how it's related to snow leopard.  So, is reinstalling snow leopard likely to help?  Would it be easier to upgrade now to Mountain Lion instead and see if that helps?
Any suggestions gratefully accepted and please let me know if there's other information that you would need to know in order to provide any suggestions.
Thanks so much in advance
Model Name: iMac
Model Identifier: iMac8,1
L2 Cache: 6
I have the same model. What I suggest you try next for this problem:
1. Run the Apple Hardware Test. It can't detect all hardware problems, especially intermittent ones like you might be having, but it is still a good first step.
2. Reset the SMC. I'm not sure why but this has fixed some odd problems I have had in the past with my 2008 iMac.
3. If this doesn't help, try running for a while without any peripherals attached to your iMac besides the keyboard & mouse. If you don't see any freezing problems, try reattaching your other peripherals one by one & running that configuration long enough to see if one of them is causing your problems.
4. If none of this helps, go ahead & reinstall Snow Leopard, making sure you run Software Update afterwards to update it to the latest version. The Snow Leopard installer isn't like earlier OS installers. To reinstall the system just run it & accept the defaults. It won't write over or alter your user data or create any "Previous System" folder stuff, so it is a fairly painless procedure. It even performs the equivalent of Disk Utility's verify disk step, so you don't have to do that beforehand.
5. If none of this helps, reply to this topic & we can suggest other things to try.
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