My laptop, running XP, Begins startup then shuts down?

I have an Iqon 1GHz, 256RAM, 10 GBHDD Laptop running XP. when I power it up it goes through two/three screens up to the XP screen with the timer bar under the logo. it stays on this screen with the timer bar moving for about a minute and then it shuts down the laptop, restarting almost straight away and getting to the same point and then shutting down again.this continues on and on.I have been told this can be fixed but not how. any ideas would be very welcome