This belongs to a co-worker. When I push the start button, the fan starts, and the screen shows quickly the 'intel inside' logo, then the XP screen, neither staying on more than a second. Then I get a blank screen with the blinking insertion cursor in the upper left (like when you are working in DOS) Nothing happens after that. If I type any commands, they do not show up on the screen.
Holding the Fn key allows me to do the normal tweeks (raising/lowering vol/mute) (screen dark/light) etc. The numbers lock light is on and It will not change.
I don't know the age of the unit. When I push the on/off button, rather than run for several seconds before shutting down, it shuts down imediately, the same instant I touch the button.
The battery has been taken out for now; just using AC.
Any ideas?

Sounds like a hard drive issue. If you have an XP cd boot to it and run the Recovery Console. Try a chkdsk /r, and if that doesnt work try fixboot and fixmbr. If all of those options fail, try a fresh install. The last option is replace the hard drive.

if the windows xp screen shows then you might be able to boot into safe mode by pressing F8 and the boot to Last Known Good Configuration. That would be the first step I would try before troubleshooting the hard drive.