Replace the video cable. I have a dv9000 as well and my video cable is messed up too. Instead of vertical strips though mine has glitchy colors that make the screen mess up and sometimes go completely out. You can buy new video cables on eBay for cheap (I need to buy one sometime as well) and it is simple to install them (take off the screen bezel, take off the speaker panel, unplug the old cable, plug in the new one, reassemble, the monitor plugs in right under the Power switch).
You could try just taking it apart and re-seating the monitor connector. The cable plugs in 3 places - the main plug on the motherboard under the Power switch, a flat ribbon connector that slides into the back of the LCD panel, and a small pin connector that plugs into the backlight inverter board. Your backlight works so I'd focus on the other two connectors. Also try wiggling the cable, especially where it goes through the hinge as the wire often gets broken in this segment due to the hinge. I was able to temporarily fix mine (still kinda works) by pulling a different section of the cable into the hinge and immobilizing the damaged section of the cable with some thick tape. I still get glitchy screen occasionally but moving the screen back and forth will fix it.
If the cable doesn't fix the problem it is probably your graphics processor. The nVidia GPU's in the dv9xxx laptops will often overheat and damage the solder. Mine did this and I had to get a new motherboard (though mine showed nothing at all on the screen). You can attempt to fix it yourself by disassembling the laptop entirely and using a heat gun to heat up the graphics processor to reflow the solder connections under it. There are several videos on YouTube that demonstrate this process.
The LCD cable connects in these locations: