計算機老是要死掉,找不原因,求助.

I don’t know if any one here can help me. My computer is PIII, it is an old system.
Right now it has a strange problem . It will dead automatically many time no any reason Just when I clicked the mouse, the mouse will jump a little and then system will dead. I changed the mouse, changed hard disk and added memory. But still doesn’t work. I think I need to changed the motherboard or CPU or buy new one. Can I get any help from here?
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