Chosen Solution

ok i turn my ps3 on and after 3 second it turn off by itself.

im not 100% sure that the psu is the problem but if that it is the route you want to go follow this guide. And you can buy a new power supply here on ebay. again im not entirely convinced this is the problem but from the information you gave it seems logical to me. Good luck and hope this helped, Cody

Had the same problem, the gpu and cpu need to be reflowed back to board and new thermal paste added.