After YLOD fix loud fan then shut off

Last week my ps3 experienced the YLOD.. I did some research and decided my problem was definately the motherboard being over heated. So I followed the instructions per fixit. Wow the dust and dirt.. I found was amazing and gross! Cleaned it all up took off the old thermal paste added new, put it all back together and it still had the YLOD :(. So I did it agian this time using a bit more heat on the motherboard. Agian changing the thermal paste. This time it came back on!! Yea!! BUT then the fan got really loud and turned the machine off with in about 30 seconds. I did some more research and found one person say I really needed to use the Artic Silver 5 thernal paste which I had not used so I went to Radio Shack last night bought the right paste. Redid the process for the third time and I have the same problem. The ps3 will turn on now but with in seconds the fan speeds up really fast and loud and then turns off.. What do I do now?? I am stumped. Thanks