PC turns off immediately after power on

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Hey guys,

Well the story is the following:
My friend told me to upgrade his PC. The specs are as follows :
Motherboard: MSI H61M-P25(G3) LGA1155
CPU: Intel Celeron G550
RAM: Apacer 2GB 1333mhz DDR3
PSU: not popular brand 300 Watts
Without any GPU

So after I searched a lot I came to this conclusion to upgrade these:
CPU: Intel Core i5 3470
RAM: Kingston Hyperfury 8GB 1600mhz DDR3
GPU: Nvidia GT1030

So I tried to first change the CPU and see if everything works fine and then instal RAM and the GPU. When i removed the CPU it seemed that it has some bend pins in CPU socket, however, his computer worked fine. So I inserted the new CPU and install the new CPU fan that I bought and also renew the thermal silicone. I did all these steps after I unplugged the PSU completely. Finally, i turned the PC on but after it turned on for maybe 3 seconds, it turned off suddenly and again automatically turned on and this cycle happened again. So I thought maybe it’s because of his BIOS version. So…

PC turns off immediately after power on

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