Boot Problem

One of the machines we have is a Soyo Dragon 7 Mainboard, with an AMD Athlon 1800+ Processor and a Western Digital 40 gig 7200 hard drive. The hard drive is the master with a DVD as the slave.
The second master is a Sony CDR, with no slave.
Thereis no Raid Assembly.
The problem, is that with a “soft” reboot, the machine doesn’t recognize the hard drive. Both CD drives show up in the POST screen, but the Western Digital does not.
If we do a power down and reboot, the machine recognizes all drives.
Any help???
We have replaced the Western Digital and the problem still exists.
Thanks,
Ken