Weird: Partitions go repeatedly missing!

This is truly weird! But before I go into details, please note that I do not need help recovering the data from the missing partitions. What I need is help in trying to figure out what's going wrong and fix it.

I apologize in advance for the length of this post, and give thanks in advance to anyone strong-minded enough to carefully read it all!

I'm running XP Pro/SP3 on a home-built box with an ASUS P5WDG2 WS Professional mobo that has worked great for years. But starting recently, all the partitions on some disk drives have repeatedly gone missing!

Here's why I say "repeatedly": I use Acronis Disk Director 11 to recover the lost partitions, which works fine (but takes hours since it has to parse through 1 or 2 TB to find all the partitions' signatures). But a few boot-ups later, all of the partitions are gone again. It's like a loop, except that it's not always the same drive -OR- controller!

I started out with 8 hard drives on this high-end workstation (all partitions are NTFS):

[ALPHA]: 3 normal, non-RAID SATA-II drives connected to the standard Intel ICH7R disk controller on the mobo.

[BETA]: 2 SATA-II drives connected to the on-board Marvell 88SE6145 RAID controller in a RAID 0 configuration.

[DELTA]: 1 normal (i.e., non-RAID) SATA-II drive also connected to to the on-board Marvell 88SE6145 controller.

[GAMMA]: 2 SCSI-320 15K RPM drives in a RAID 0 configuration (which hold my boot partitions as well as others) connected to an Adaptec PCI-X SCSI-320 RAID controller)​

Here's the history of this problem:

(1): Roughly two weeks ago, I discovered during boot time that the Marvell BIOS reported that it could no longer find the RAID 0 array definition for [BETA]. Windows couldn't see it either.

(2): All SMART tests and diagnostics on all hard drives, including [BETA] and [DELTA], passed perfectly. There was absolutely no indication of damage other than the missing array definition. Since I could find no hardware problem, I assumed the Marvell controller had failed. I unplugged the SATA RAID drives ([BETA]) to avoid any further problems with them. Note that the [DELTA] drive and all partitions were perfect.

(3): A few days later, after booting up I discovered that all the partitions on the non-RAID drive connected to the Marvell ([DELTA]) were missing and that it was marked "unallocated"!

(4): I then connected [DELTA] to one of the SATA ports on the ICH7R (since I assumed the Marvell had failed), then ran Disk Director 11 to recover the partitions, which worked fine. I left it on the ICH7R (there were now no drives still connected to the Marvell controller).

(5): A day or so later, I found all the partitions gone on one of the other drives on the ICH7R!

(6): Disk Director 11 recovered all those partitions, too.

(7): Later, all the partitions on the drive from step (4) disappeared again!

(8): I then recovered those partitions yet again!

(9): I just booted up to discover that all the partitions on yet a third drive connected to the ICH7R were gone now! (DD 11 recovered them, too).

The only drives that have never lost partitions are the 2 SCSI drives connected to the Adaptec! Also, I just finished running Kaspersky 2010 with maximum settings, but it didn't find any malware at all.

What on earth is going on?!? PLEASE HELP!