I have seen numerous times, on a co-workers laptop, where XP Pro will not
start up properly, doesn't show the logon screen. The machine goes through
the boot process successfully, all the BIOS screens are good to go, but the
OS doesn't seem to fire up. He will then restart the laptop and usually the
OS will start up properly on the 3rd reboot. His machine has anti-virus
software and it is run regularly from our anti-virus server, and anti-spyware
software, his machine is clean of spyware and viruses.

Any ideas?