Screen and power down?

My laptop was working fine, then all of a sudden, lost the picture and power sound, power light still showing, but that's all. I switched off then on again, all seems ok for about 10 seconds then the power sound dies.

Spec:
Advent Modena M200
Intel Celeron T3300 2.0ghz
2ghz DDR3 RAM
Wndows 7 Home Premium

All help much appreciated