Nvidia event viewer?

If it's turning off without a bluescreen or warning, chances are high that it's hardware related. Is there anything that triggers it?

How do you know it's your gfx causing the fault?

Im sure its my gpu since i stress test my hardware and my gpu does not last 5 seconds during stress test. Cpu and other components finished the stress test without any random shut downs.

And yes, My computer shuts down without warning ( no blue screen, screen just turns black for a second then shuts down). My gpu runs a max of 68 degrees Celsius.

Thank you for your reply

No worries, hm. I had a similar case with an (desktop mind) 8800GT, would freeze and crash the PC under stress test, but sold it on Trademe as faulty (think ebay) and the guy was really happy with it and it works perfectly.

So don't give it up for dead.

I would invest in a can of compressed air, and blow out your intake holes on the underside of your laptop, just please be really carefull not to blow too hard and make the CPU fan spin erratically, as this can damage bearings and make it really noisy, so quick sharp controlled bursts of air might be best.

As your heatsink in a laptop starts at your GPU, then goes to your CPU and then to the fan, the GPU can get quite toasty under any stress testing, and from what you're saying it *sounds* like it's merely overheating.

If the can of air doesn't dislodge enough crap from the fine heatsink fins it may reoccur, in which case your next option is to to take it into a repair shop and spend upwards of 100+ getting a technician to take it apart and replace the heatpad with some high quality heatgoo. Not reccomended you try this yourself, as A. most laptops have at least 20-30 screws before you get to this stage, and B. due to size differences between the heatsink and GPU, the heatpad may be quite thick and if you damage it removing it, you may not be able to replace it, it would be a call for a professional to make who may have the right tools and expertise to make that call.

Sorry for the rant, but just making you're well informed.  

Thank you so much for your reply. Well my fan is fine, its cleaned very well. I have replaced the stock thermal paste with high performance paste and did its job. Well unfortunately its quite difficult to find a can of compressed air in my country, I used a very soft brush instead and i guess it worked well. Right now my Max temps are 72 C for CPU and 68 C for GPU. Well taking the laptop to the repair shop or having a professional to do the job will be my final option if i run out of fixes that i could try. For the mean time I'm researching if voltages could be a problem, like maybe my gpu just needs a little bit more voltage to make it work perfectly at default clock speeds. Oh and i tried looking at the event viewer in the control panel, unfortunately i don't know whats the right message that would tell the exact reason (I see tons of stuff). Thanks.