Software update, Safari and itunes will not startup

Hi I'm new at this and have a little problem with my MacBook 13".

When trying to startup safari, software update, itunes and google chrome they all crash and close all tho google chrome stays open but will not go on the net.
I took it to the apple store were they told me it was a problem with the graphics chip and the logic board needed to be changed it was still in warranty so it was fixed and given back to me and everything was working but now about 6 months later all the same problems are back.
I have been told in the apple store it is now out of warranty an I will have pay to have it fixed. Now I'm no expert but how would this be a problem with a graphics chip?? Last night I clean installed mac os x but the problems remains I setup my mail account and received over 3000 emails which took about 40min with not a problem any help would be really help full.

Need more info how big is the hard drive and how much free space do you have.
Also have you shut the computer down for 30 seconds not just restart or sleep?
How many things do you have open at the same time?
Is everything software wise up to date?
Are you running any form of anti-virus ( a major cause of problems and not needed)?
Can you print the log showing the crash?

Hi there is a WD Scorpio black 500GB with a clean install of os x snow leopard so over 450GB of free space.

The Mac has also been shut down for more than 10mins

There is nothing running on first boot after the clean install I get the first error from the software update telling me apple software update has stopped working and crashes. I go on to try itunes and safari but with the same errors. It is deff connected to my WiFi and I connected my mail account and it received all of my mails without any problem.

As for the software being updated I can't do it as it crashes I am not running any anti-virus and I will try and get the crash log printed and posted tomorrow.

I am wondering do you have any thoughts on this being a problem with the graphics card or any other hardware??

Thanks for your reply.