I have a new computer, custom built, with Windows XP Pro, AMD Athlon 64 x 2 dual core processor, 2GB memory, RAID configuration with two SATA drives, and two additional hard drives, one a 500 GB SATA drive and one a 160 GB IDE drive in a removable tray. Here's the problem. Either one or the other--or both--of the extra hard drives will "disappear". The system doesn't see them at all. Sometimes this happens after it's been in sleep mode, and sometimes it happens out of the blue. If I reboot, voila! there they are again.

Does anyone have any idea why this is happening, and how I can fix it?