Catastrophic Media Failure or Data Corruption

[Millard]

My Windows XP PC boots into the familiar log-in screen
with multiple users. However, now it's asking for a
password for each user, where it never did before.

Also, after the log-in screen, I get the following
messsage, "Catastrophic Media Failure or Data Corruption
has Occured". Does anyone have any ideas on this and how
to resolve this problem?

Thanks!