You should be able to see any SATA drive connected to your system in Disk Management and Windows. You should also be able see these drives in a BIOS (assuming you have two BIOSes reflected).
I don't know how your BIOS works with the RAID. With my PCI card, I wind up with two BIOSes and drives attached to RAID controller will show up in Disk Management and Windows.
I doubt if they don't show up...is a PS issue. But that can be checked by looking in Event Viewer...and by reducing the number of drives and steadily increasing.
I have a 500-watt PSU and I have had as many as 7 hard drives and a DVD-writer attached to my old XP 2800 system...without problems.
With the SATA drives, you might need to check your connectors...they are not as stable as IDE connectors, IMO and can easily be inadvertently loosened.
Check Event Viewer for info on drives, looking for errors. You can also check for info on possible PS issues.
What is the Event Viewer, and Should I Care - Ask Leo! - http://ask-leo.com/what_is_the_event_viewe...uld_i_care.html