Internal hard drive does not show up in win 7 explorer

I installed windows 7 dual-boot with vista ult 64-bit. not a problem. both versions boot and run. however I have installed 6 sata drives. vista recognizes all 6 in explorer and device manager. windows 7 however recognizes all 6 in device manager but will only display 5 in the compter drive explorer view. there is no method to access the (actually 5th sata) 750gb drive. it cannot be accessed by any program I've tried so far. it can be seen by speeddisk 10 as an unmounted drive, (not gonna try to access it tho)(xp also recognized and accessed all 6 drives)
I did have have vista on the sshd and it showed all drives. Any ideas anyone?
hardware:
asus rampage formula motherboard,
4 wd 320 hd drives,
1 corsair sshd 6th in sata chain (windows 7 installed on it)
750 wd hd the 5th sata which is not accessable.
8 meg corsair ram
1000 watt corsair ps
asus 4850 video card.
running in non raid mode for the moment. I am not impressed with 7 especially since being screwed by the lack of the ult upgrade option, but that's just an vitrolic opinion.