XP machine scandisks EVERY boot

What do I look for to correct a problem with a computer using Windows XP Home O/S from running scandisk at EVERY boot up even though it was shut down properly?
This computer is one of 4 identical systems built in our shop and delivered to an auto dealership.
It is the ONLY ONE out of the 4 with this problem.
ALL MS Windows updates were downloaded and installed at time of assembly.
A search of MS helpdesk only produced hard drive cache fix for Win 98/ME when encountering this.

Any help appreciated.
Thanks