My colleagues and I work in a tech environment and we have seen several computers with the same symptoms. Namely a failure to boot xp. After the xp logo screen the screen goes to blank and it just hangs.

This looks like a graphics card fault but changing card does nothing.
Booting into safe mode and it stops at agp driver.
Repairing windows gives a lsass.exe error which cannot be resolved.
Scanning hard drive reveals no viruses.

So far we have had to reformat and reload xp - but I just got another computer with same fault symptoms. I'm wondering if anyone has similar findings and have they discovered cause/fix.
There is a small possibility that an av update may have been cause, but no way to confirm this.

Try to cheek all the system component and detect any one that have from power supply unit

Below is what I posted on another board... perhaps a SP you're applying is corrupt? Or is not finishing properly/getting interrupted? I would re-download the service packs you're applying. If you're using an UA disc, then perhaps back to the nLite drawing board?

--

I didn't put the two together right away because it worked fine for a couple of restarts, however, then the screen on this XPS M1210 went blank as described above. The culprit turned out to be the installation of Service Pack 3 (SP3). Apparently during clean-up, the tech working on the issue thought the installer froze, or was in a loop as it was "Cleaning up" for the better part of an hour. They force quit and then restarted to find that SP3 was installed and there were no error messages reported. They thought their job was done and the case was closed until the startup problem arose.

I had to go back and figure out the problem and decided to use System Restore to roll-back to a date prior to SP3 being installed. That completed successfully, I then reinstalled SP3-- this time I waited the hour for the clean up to finally complete. I then rebooted the system and it started up fine. Since then I have restarted multiple times and it looks good so far (it's been 3 days). Updating the video drivers will not work and you will be wasting your time trying to find another fix... I hope it works for you!
-MR