Well first you should get a monitoring program like Everest / Coretemp / Realtemp and see wich component is overheating. You can buy an aftermarket cooler for the cpu/gpu or a new case if yours lacks airflow.
What are your temps? (speedfan) Most likely you will need to remove the CPU fan, clean the CPU and fan, then reapply thermal paste, then remount the fan. I would also monitor your voltages (speedfan as well).
I guess , my graphic card is creating the problem..
its of 64 MB only..
or should i try changing d fan....?¿?¿
and YES... at the moment that it turns off... a foul smell of something burning comes..... nd it vanishes... evrytime