I can tell you I wrestled with this problem for ages. I had this start at some point without much warning and I thought I was losing my mind. I reinstalled XP, then I installed Vista, then I tried to run all sorts of driver, generic, nVidia, nothing helped. The computer would start, the screen would be grey or show vertical stripes along it. I knew it was not a screen issue because twisting the LCD did not appear to make any changes, I also knew it wasn't the initial wiring because I checked the connection about 50 times along the way.
What I ended up doing is.
1.) I took apart the laptop as per Dell's instructions online, there are several steps, about 20 screws, it's not difficult if you are brave enough to do it. It's very difficult to break anything in a laptop unless you are especially forceful and careful to unscrew everything before prying things open.
2.) I took off the heating core for the Intel Processor and the nVidia chip as well.
They are two long copper tubes leading to a very fine heating core which combines beside the fan. The whole thing needed a bit of dusting so I naturally did that.
3.) I carefully cleaned the top of both processors, they have a very smooth surface which is supposed to flawlessly contact a heating distributor and carry the energy out into the fan, there was a grey insulating paste protecting the chips edges but it had gotten between the core and the copper, causing lack of transferrance. Do not leave any oil or residue on the chip unless you want your computer to turn into a bacon pan.
4.) I replaced the heating core and placed a copper coin (penny or whatever) on top of both heating distributors where the chips would be, I put a tiny piece of hockey tape to keep it from wiggling, this is to create more pressure onto the chip as well as a little bit more room for the heat to distribute through the air. It worked perfectly, my chip slowly recovered and I am playing Starcraft 2 on it without a hitch.
I'm glad I got through this, it's not the end of the world !
5.) I said a little prayer.