Help! my windows XP Stucks regularly

Hi all,
I am using windows XP OS and my computer is an old one(pentium 4). It used to work without any trouble. But from several months it stucks when working. At the movement I can’t use the computer because it stuck within few minutes from strat. Processor temperature is indicated as 70 C(aproximately). I have installed 3 RAMs(512,256,256). Motherboard is gigabyte. If anyone can help, I am so gladful. It is not possible buy a computer at the movement.

Thanks
Manjula