I had a early 2011 Macbook Pro 15 inch with 2.0GHz CPU, 128G SSD and 8GB RAM. Everything apple stock. Two days ago, the computer suddenly crashed with the display pixelated and splited. I was running a statistic computation during the crash, which uses 12.5% CPU. After that, I cannot boot into the OS. The apple logo will appear and then stays at the grey screen forever. I tried recovery mode or safe mode or boot from a bootable USB, none of these are successful and I always get the apple logo and then a blue screen with blue and black vertical strips. Resetting SMC or PRAM does not help. I can boot into the single user mode and I can use target mode to copy all my data out. I also tried taking out one RAM and putting it in different slots. That does not help either. I ran apple hardware test several times, both standard and extended. No trouble found. I ran fsck -fy on command line to check the hard drive, no trouble either. Yesterday, I reboot it from single user mode and successfully boot into the OS. Since then, I can always boot into the OS and do normal light duty work, like email browsing. The computer behaves normally and nothing is sluggish. I can hook up to a cinema display and do the same work. But if I put a slight load to CPU (like running a R code using about 1/8 of CPU) or GPU (like playing a youtube video in 720P), it will crash. Then I can boot it again when it is cooled down. I cannot boot it right after crash when it is hot. I looked at CPU and GPU temperature before crash, around 80 is the highest I see and the fan speed goes up correctly. I saw a long thread in Apple forum talking about the crash in 2011 MBP but my case seems to be a little different. I am confused as why it works fine with all the programs but cannot handle any stress. Would it be a cooling system issue or would it be a failure in CPU and GPU? It is odd that both CPU and GPU fail at the same time. Or could it be a software issue? All the software and firmware is up to date.