Dr Jezz is spot on. Read the article he has posted I've had exactly that issue.
I took my 2008 mac book pro 15" to an approved apple 'plug in a usb sick and replace the part' centre, but of course, because the mac wouldn't power up they couldn't establish what the fault was as they couldn't run their diagnosis software so the easiest thing for them to do is replace the logicboard for £550 😠
I spent half a day speaking to Apple UK, advisors and team leaders and to the 'replace' centre staff explaining to the what the fault was and asking them if they would look into it. I got a resounding NO from Apple who did all they could to put the responsibility of the known fault onto Nvidia.
Anyway I'm managing to type this as I've just got my mac book pro from an idependant repair centre in Leeds and they confirmed and fixed the Nvidia fault for £120! The guy there also said he had seen 10 already this month with exactly the same fault! I'm happy with the service they have provided, they've saved me a **** of a lot of money but Apple should be embarrased at the lack of customer service they are providing for this issue.
I've got a very bitter taste in my mouth after dealing with Apple on this occasion.