After 2 second I turn on my ps3 it shut down

Hi guys! After I turn on my ps3, the fan spin and it shut down after 2 seconds. I know that the PSU might be faulty but i tried tested other things. I tried to turn on my ps3 without the hdd but nothing happend. After this I dissassembled my ps3. I tried to turn on my console by putting pressure with my finger on cpu but nothing happend. After this I tried to put pressure on gpu and a grey screen showed on my TV and my console beeped 3 times. So...should i replace my psu, reball or replace the gpu, just replace the thermal paste and clean the fan or you have any other idea?