RAID Card & associated Hard drives disappeared

Well I thought I'd solved my back-up issues.
But I was wrong it seems.
I have an early Intel MacPro running 10.6 with 4 hard drives installed.
I have two 1TB hard drives mirrored as a RAID and using TimeMachine to backup the other two Hard drives. This has been working well for around a year so far. Today though, TimeMachine failed to back-up. The two 1TB hard drives (RAID) have disappeared completely and the System Profiler tells me that I don't have a RAID card installed. I know I do have a RAID card.
I have read in various forums about the RAID card battery failing - could this be the issue? or could card have failed? and why can't I see my two 1Tb Hard drives? I have used Disk Utility, Disk Warrior and Data Rescue to see if I can find my two hard-drives and can't.
Has anyone any idea as to what has happened and how to fix it. I find it inconceivable that both hard drives have failed at the same time as the RAID card. Any ideas?

I would try System Profiler to see if the card is "visible" as it should show up in the PCI area. If it does not show then perhaps the battery has gone or the card had come unseated.

yep done that

I've checked the system profiler and it says "This system doesn't contain any supported hardware RAID devices." I also didn't get any low battery warning - it just disappeared along with the associated hard-drives.

Long shot idea is to re-apply the last Combo update just in case one of the latest updater killed a file. Is there any software you installed for the RAID card? My AIO scanner just failed after the latest 10.6.5 update and then the revised software from HP fixed it.