Inspiron 9300 PROBLEM!!!

       Hi all,

               Ok, I have a problem with my Inspiron 9300 Laptop computer. The problem occurs with the attached LCD wide display monitor. When I boot-up my computer for the first three seconds its fine. And everything is normal, and it displays that big blue "DELL" logo in the middle of your screen. But as soon as that logo disappears and my PC starts loading my operating system. The whole screen dims, so its like someone turning off the lights at night. I've tried everything, I put the LCD screen on "BRIGHTEST" in BIOS mode, for both AC, and Battery, I set my LCD monitor to the brightest using the: "fn" key and the up and down arrows. I changed my system power scheme to "ALWAYS ON"(witch means that nothing will turn off including the monitor.). I reinstalled my graphics driver, I set the screen saver setting to: "off", I even tried system restore! But it still doesn't work. My battery is working fine(I checked at system BIOS, it says: "Battery is healthy"), My AC is in near perfect condition! I have tried plugging my laptop into a external monitor, and it works fine the colors are true and there is no problem. However I bought a laptop computer, and I want a laptop computer instead of a desktop, so thats not an option. Yesterday, I don't know if it was luck or something, but at like 2:00 P.M. I tried booting my computer again. AND THE LCD SCREEN CAME TO LIFE! It worked! =3 I played a game of Gunz: The Duel, and it was still working. It worked all the way until almost 10:00 P.M. When I pulled my AC plug. Then it dimmed again:/. That leads me thinking that there is probably like a time system in my computer. Witch is telling the computer to dim the LCD monitor. I don't know if such thing exists but my computer seems to have more chances of working in the afternoon than in the morning so thats how I came up with that theory. Unfortunately I bought this computer in 2004 so the warranty has expired, and I don't have the money to buy warranties. 

My system Specs are:

Intel Centrino Processor@ 1.60 Ghz

1.256 GB of Dual-Channel Memory

ATI X300(64 MB) Graphics Card

17" LCD Display Monitor(attached to the laptop)

Windows XP Home Edition

Sigmatel C-Major Audio Sound Card

ETC.... 

NOTE: Please help me step by step, on what to do, because I am a 13 year old kid that isn't to good at computers. I tried describing everything as detailed as I possibly could. I WOULD LIKE TO THANK EVERYONE THAT SPENT THEIR TIME READING THIS POST, AND HELPING ME SOLVE MY PROBLEM. AGAIN I REALLY APPRECIATE IT. Sorry for any geammer and spelling mistakes that I made. ^_^