Wierd XP issues

I just talked to a client over the phone, who described the following problem:

Took desktop computer on a road trip (needed for some work during vacation at in-laws)

Brought computer back home... plugged it in... booted it up

Computer would not boot into the log in screen, displayed an error (he wasn't able to write down the error name), and restarted

Computer would not boot into safe mode

Client checked make sure that hardware was seated properly

Computer still wouldn't boot up

Inserted the windows startup disc and ran the recovery console, windows found an error, fixed the error, and began booting up

Windows booted up into the desktop, and started loading drivers

While loading drivers, an error message came up (he was only able to catch something like hal______.dll) and restarted the system

NOW... when he boots up.... all of his user accounts, including admin, are gone... recovery mode won't work.

Anybody ever had this happen before?

I recommended unplugging different hardware, and trying again, but I think its a little late for that. Also, he knows he can just pop the drive into another computer - retrieve the data - and reformat. But he is holding that as a last resort option.

Thanks for any help in advance,

Jdrake90