So what about your failed disk; did it fail completely? Then your data is gone. If its still being detected but has some surface errors, you can still recover your data, either with proprietary Windows apps that understand RAID, or using Ubuntu Linux livecd.
Sub mesa is right - the only way to recover your data will be if you can get the disk operational again. Try disconnecting and reconnecting all of the cables to see if that's the problem. You might try swapping the cables between your two drives to see if it's a problem with the cable itself.
If that doesn't work, I've seen posts that suggest putting the drive in the freezer overnight can sometimes shock a drive into working for a while. If you plan to try that, then be prepared to transfer your critical data off the drive as soon as you get it up and running - it may not last for very long.