Monitor Black Out

When I start my Dell Inspiron 5100, the screen is fine for first 10 or so minutes and then turn black. I can see the stuff on the screens by shining torch or other light. Sometimes the screen comes back after like 20-30 minutes. There is more to this problem. I had blue screen with this laptop before I had this problem. I left my laptop with blue screen untouched for four months and when I booted from Windows XP CD, the blue screen got fixed, but this screen black out came up. I am not sure if my screen has died. Any idea what’s wrong with my laptop? Any simple solutions?

Thanks for any help!