Windows XP - three user accounts, one keeps reverting to default settings.

[Puffin]

What the title says. My mom's user account has reset itself twice now, over the period of three days. We still have all the files in the C: drive, but on the account itself, the desktop, itunes settings, etcetera are erased. We kept having to redo everything. What could cause this? Insightful answers all get a thanks... If that'll help you to help me.