Cpu automatic shut down

[dhootha]

Hi everyone
I use a 5 year old system(Desktop). Recently the cpu started shutting down automatically .When i try to restart it logs on but again the cpu gets off after a few minutes. I see the led stops glowing and fans stop working when i mean cpu shutting down. But i see the power to monitor and keyboard and mouse is still there.
Every time i open my system, I couldn't use it for more than 20 minutes. I couldn't turn it on immediately again (It can't stay for more than 5 min). However i tried to run to some temperature tests through speedfan software.

I have already tried removing the ram chip(I have only one gb) and putting it in the other slot.still the problem persists.
Here are the image links. Sorry, I didn't know any other way to share this pics.
https://www.dropbox.com/s/urwfqexqtuvgiu2/1.JPG
https://www.dropbox.com/s/qf29ob7qghbj841/2.JPG
https://www.dropbox.com/s/amtw53pqomdf631/3.JPG
https://www.dropbox.com/s/gg8e59249jtxb7c/4.JPG

windows xp
I have intel core 2 duo processor.1 gb ram. gigabyte motherboard g31m-es21.I hear no unusual sounds when it shuts down.I have cleaned my heat sink and turned on the system.
Let me know if u need anymore details. Please Help me

 

[notlim981]

5 years, probably your psu has called it quits, have you tested it on another system or have you tried another good working psu in yours?

 

[InvalidError]

Core2Duo with stock HSF? Check your CPU temperatures with CPUInfo Hardware Monitor or similar utility, your CPU might be hitting Thermal Trip due to the stock HSF loosening up over time.

 

[dhootha]

Best answer selected by dhootha.