There is a good chance Avast is causing your problems, not only is that a waste of time, system resources and possibly money antivirus apps on OS X machines will tend to create more problems than they solve. Locate the uninstall instructions the developer recommends and uninstall Avast and any other anitivirus or "performance enhancing" apps which are almost certainly bogging down your computer.
My suspicion is you recently switched from MS Windows and have carried your bad Windows habits along with your Mac.
Your suspicion is wrong. I can't stand Windoze. Been on Macs 9 years. I had a specific task for Avast - and it achieved that. But it certainly crashed my computer this time - after I stopped it completing its tasks.
Anyway...I can't get into the applications to uninstall it - or I would have done that. At this stage I can't even eject the Snow Leopard disc. I have a dead parrot. I don't want to have to take it to the shop. I would prefer to fix it myself if possible.
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Thanks Eric...I had thought of that but I only have a Macbook 6,1 - with no Firewire and no Thunderbolt port.
In Safe Mode I managed to get the dock, desktop and most of the Applications to load. It appears to still have my files and photos. I connected an external drive - which it recognized - it asked if I wanted to back-up my Hard Drive using Time Machine and the external drive... I clicked...and got the dreaded beach ball and it froze for an hour or so.
I'm trying to avoid having to take it to the shop and be burgled hundreds of dollars.
Bloody Avast - that's where the problem lies. If I could just get into that and turn it off and then trash it. And...if I could at least save my documents and photos...