2008 macbook pro nvidia defect

I have been where you stand. I lost my first MBP to the nVidea curse. The problem is not related to the safety shutdown routines built into all Macs that protect them from temperature spikes.

The problem was that the nVidea Geforce 8600M GT chipset was improperly made by nVidea's suppliers and were defective from Day One. Eventually, some overheating event causes the GPU chip to physically degrade and fail.

Apple had a repair extension program that covered this but it expired in Dec 1012. Mine did six months after that deadline.

In short, this is not recoverable. The only proper fix is a new logic board and the supply of new, unaffected boards was pretty much wiped out by all the failures. Most repeir boards still has the defective chip. Any offered on the used/pulled market either have the defect or will get it.

That fact that yours took 12 year to fail is miraculous considering how many 8600M Macs failed the first five years. Think of it in terms of a large-breed dog that has an avarage lifespan of 10 years. Were your computer that dog, it would have lived to 24 year old!

Time for a new computer.

Try running the Apple Hardware Test.

Try booting into Safe Mode.

Try forcing the laptop to use the Intel GPU instead of the discrete NVidia GPU which is known to fail on this laptop.

gfxCardStatus app:

https://github.com/steveschow/gfxCardStatus/releases/tag/v2.4.4i

If you cannot use the gfxCardStatus app, then here are some other links on how to force the laptop to use the Intel GPU:

https://github.com/steveschow/gfxCardStatus

http://dosdude1.com/gpudisable/

You may also want to check the health of the hard drive by using DriveDx. Post the DriveDx report here using the "Additional Text" icon which looks like a piece of paper.

To check for possible software issues run EtreCheck and post the report here using the "Additional Text" icon which looks like a piece of paper.

"I know that this machine is known to malfunction, but when defective, they usually don't boot."

Actually, this isn't accurate. When that GPU starts failing, you may see any number of symptoms. I saw one once that reported a 3TB home folder on a drive that clearly was a 250GB hard drive. There are many weird issues that start to crop up even with the machine otherwise booted to OS X. That said, that GPU will inevitably fail, much like the AMD Radeon HD 6000M series on 2011 15" and 17" MacBook Pros. My honest advice would be to sell that thing for parts.