XP question

Must be our week for computer problems.

My daughter showed up tonight lugging her computer. "Fix it Mom!" LOL

But, I don't know what to do so any suggestions would be welcome.

It starts to load Windows XP, but then this message comes up:
"The system is not fully installed. Please run setup again"

Here's the kicker. I asked for a disk, she didn't get one with the computer when she bought it. I thought maybe she just couldn't remember, so I called a friend who has an HP computer running XP, and he said his didn't come with a disk either. I would think they had to send a disk. I can't call for support because she didn't think it was necessary to send in the registration/warranty card when she bought the computer.

So, short of having to buy another windows XP program, is there any way I can get past the above message and get into windows or somewhere to run setup again?