I had a similar problem recently in a laptop and when I reinstalled windows it then would hang during hardware installation.
Since I had recently replaced a LAN/modem card, I removed it for the reinstallation and had no problems from then. I then put the card back in.
Seemed to be a problem with the driver for the LAN/modem card.
I would suggest you remove all hardware including sound cards, modems etc to see if you get it to start before you try reinstalling.
BTW, if you do find you need to reinstall, check out this article which guides you through a repair install.
http://www.michaelstevenstech.com/XPrepairinstall.htm