pc shuts off at windows splash screen

[Loraphet]

I have an 8 year old system that was XP os. hadn't turned it on in afew years. Turned it on it was slow, so I decided to upgrade hdd and os. Bought an WD blue 320gb 7200rpm and win 7 pro 64 bit. Installed and at the end of installation booting for first use the pc shut off. Got it back on ran for 2 hrs loaded Wot and anti virus and shut down. Turned it back on later and it shut off at windows splash screen. I replaced the ocz fatality 550w psu with a evga 500w one and it worked for acouple hours I shut it off and when turned back on shut down at windows splash screen. Keeps shutting off. I am deciding on just buying a new case mobo and cpu and maybe ram but i would like to try to understand what happened. Any advice or info is appreciated. I am avg with computers built my 3 systems myself with friends. never posted here but have read alot threads. : )

mobo=abit ax78
cpu= anthlon 64x2 5000+
4gb ram
gts 250 video card
old dvd {ribbon connector not sata}

 

[maxwellmelon]

have you checked cpu temps. old computer prob has old thermal paste. when cpu gets to hot it shuts system down for safety. (also said computer was slow which could be thermal throttling before it gets to the shutdown temp)

 

[Loraphet]

When the computer was up both times for about 2 hours I had coretemp running. wasn't show any temps above 50c. I don't know if the graphics card would cause the system to shut off. or what other pcs of hardware would cause it besides psu. I had replaced the paste twice before last time maybe acouple years back. When repair did make it through at one point it had a message about hardware failure. Could the new hdd be bad and cause the computer to shut off?

 

[maxwellmelon]

Doubt the hdd is your issue (it would have to have a short just about to cause a PSU to turn off and well you can get into booting so doubt that's it as a short would power down the psu very quickly) don't know what it could be as even memory faults would BSOD it wouldn't just shut it off.

Good luck. I got no more insight