when you boot your system and get the "No Operating System Found!! "message it means that either 1 of the 4 key startup files are trashed or your HDD (hard drive) has some serious sector problems where some of the OS startup files are located. Question for you about the laptop would be "Did you ever here any strange sounds coming from the HDD?" Also did you keep your Anti-virus dat files up to date? There could be several possibilities. But as someone has suggested but not quite right, Start your laptop with the Windows XP CD (if you have it) and boot from the CD and run the Windows XP recovery. Sometimes this will work but in my experience the possibility is slim. If that doesn't work, then its a trip to your local Computer repair place to have some expert assistance. Hopefully you still have a warranty on the thing.

Post what your results are and I'll try to help further....