Computer stucks

hi i have p4 computer mother board intel d865gbf 2.4 g proceser intel celeron g force fx 5500 256 mb nvidia card 768 ddr 1 ram problem is that when i start computer after some time loging in it stucks and every thing stop working computer is still on i checked it but i am sure it is hardwre problem but in which part i dont know perhaps in video card or power supply or somthing else .can any one help me.plz

 

Have you checked for overheating? What does event viewer say. I have no idea, just throwing things out. Which OS?