If you restored the OS from the Dell CDs.
When I see a machine like that I reach for my Ubuntu LiveCD (see bing, google) so I can boot up another OS without installing that OS. That helps determine if it's an OS or hardware issue.
Given so few parts in laptops to change, you always do this test.
I am using a Dell XPS M1530 laptop with Vista Home Premium. Very recently, when I turn on this laptop, the screen will not turn on. I am forced to turn it on and off until it does, which can take up to 30 or more tries, it seems to be more every time.
The thing is, the custom desktop I was using before this with XP had the exact same problem. As I recall it was especially bad when it was the dead of winter and the room was really cold, but it's 80+ at any given time now so that can't be it. I swapped video cards (both nVidia and ATI) and PSUs in that machine, but nothing changed. The monitor worked on other computers. The only thing that fixed that was a reformat.
So, any ideas on what this could be and its cause?