mobile sempron on asus laptop

has anyone changed a mobile sempron cpu on asus laptop, the comp has been overheating and cutting out,took it apart and found cpu to be slightly damaged.
The funny thing is that the comp still boots up but cuts out soon afterwards,especially when u plug in the power cable.

Ive done many cpus on actual computers but not laptops and any time ive had a prob with them u wont get them booting up at all whereas with the laptop u do, its a first for me.

Anyway im struggling right now,i went and bought one second hand from ebay,in better condition than the one thats in but still a slight bit of damage and the same happened again, will boot up and then cut out and cuts out faster when u plug in the power supply.

The cpu is the mobile amd sempron 3000+, havent been able to find anywhere that sells them new.

Has anyone had experience with this model of laptop and similar problem, your experiences would be very helpful in case im doing something slightly wrong. I know how to apply paste and clean them to prep as i said earlier just not with laptop versions.

cheers gio