That means the HDD and all is likely ok. But any error on any XP Operating System file and it will not boot. You may want to reload the Operating System then restore your files from your backups.
Bob
I have an original model of the Dell XPS laptop (circa 2004), and running XP Pro. When I press the "on" switch, it will turn on but not boot. I have run it through the diagnostic tests, and it passed all tests. I have also tried to boot it from the disk, but no luck. Does anyone have an answer to what the problem could be? I doubt that it is a virus, as I run virus scans every day with AVG, and they have all come back clean. I had one friend tell me that it could be a problem with the on/off switch, and another tell me that it could be the mother board. I really cannot afford to take it in to a shop, as I am retired and living on a very tight fixed income budget. I would appreciate any answers that may be out there. Thanks.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic