XP doesn't bootup, but doesn't fail either

Trying to help my friend.
I turn on his PC and it shows the initial boot screen, then goes blank and I just get a blinking cursor in the upper left corner.
I can get to the setup screen just fine and I can boot-up with an XP Install disc (but then I abort the install).
Is there any risk to re-installing XP over the existing version? (I don't want to lose any data or configurations). just double checking

Thanks

You could try a repair install. Follow the instructions from the link below:

http://www.webtree.ca/windowsxp/repair_xp.htm#How to Repair Windows XP by Installing Over top of Existing Setup:

Caution!! If you see anything about formatting quit and start over. A repair install will leave all files, documents and photos intact, but you will have to reinstall any service packs, not included on the cd.

Scroll down a bit on that page and then click the "How To Run a Repair Install".