PC shutting down itself

[Senkyyy]

Hi , my PC keeps on shutting down itself , idk what to do. First time , it seemed like it only shuts down when ethernet cable is connected , so i tried buying new internet card. Worked fine for around 2 days , then the problem started occuring again. Next thing , my 350W PSU blew out , so i bought new one , 450W. Worked fine for around 1 day. Then started occuring again..:/ Sometimes it shuts down even be4 bios , so i dont think this problem might be software related.Tried new cables, didnt worked.

Specs:
CPU: AMD Athlon 64 x2 4800 @ 2.4GHz
RAM: 4GB (2+1+1)
GPU: Nvidia geforce 650Ti
OS: Windows 7 Ultimate 64bit
PSU: 450W

Any advice would be greatly appreciated!
Forgive my bad english , i am not native speaker

EDIT : Tried unpluging CDDRIVE and HDD , still shutting down.

 

[wllmgrms]

Process of elimination lol. You have an older CPU/motherboard. One of those MIGHT be going bad... someone else would have to chime in and back me up on that or tell me I'm wrong. You can attempt to put on one stick of RAM in at a time to see how it runs; insert one stick, power it up, let it run, see what it does, shut down, try the next stick.