Power problems?

I have a Presario 2700 laptop. I had it to a computer repair place and they told me it just needed to have the information restored from the original restore disk. That did not work as I tried to do it. I reformated it and installed Windows XP. The problem is that the computer boots up and seems to be working fine and then just shuts down. I have run it with the battery out and in - no difference. I have run it with the power supply hooked up and not hooked up - no difference. Can you help me?