It sounds like a driver issue - i had this issue with my laptop when i installed windows 7. I installed the driver it was fine.... it may not show up in the device manager..
I would look at the manufacturer's website and download all of the drivers for your computer.
Well, then it probably the age thing, and damage on the inside.
I had an issue with a dell at one time where the motherboard had cracked and the sound card a few other things stopped working....
Does the laptop get thrown around a bit? I had this issue with a very old laptop... and i threw it around a bit... and it just went on the motherboard....
OK a few things.
- Your most likely going to be getting a 15.4 inch screen if you want decent specs.
- You can not get a decent laptop for what you want to do with your budget.
- The battery life, well you might as well get a mac! A PC will not do 5 hours minimum!
- You need a bigger budget.
Google normally helps ;)
A quick search gave me http://www.mobilewhack.com/hp-hdx18t-a-184-inch-laptop/ and it doesn't seem to have a Dual Layer... and all the other sites don't have much info.
The specs aren't the same, or even any better.
The one you provided above, has a slightly less processor than the others, hard drive isn't as big, screen isn't as big, but it does have a better graphics.
Sounds like something has died along the way.... and has been affected due to the water involvement.
Otherwise, i got no idea, sorry.
Maybe try another video card???