ACard is ATA, not SCSI, though System Profile may show it as 'scsi' interface in Panther. Does it have the latest firmware? Sometimes a update to OS X can do more under the hood and it is only later that users find out, which has resulted in those "firmware RAID" cards breaking. They are usually safer to use as Apple Disk Utility RAID or just use one drive for your system, 2nd drive for /Users and media, and use native IDE bus for backup or iTunes and 2nd system.

In the Troubleshooting/Help Forum threads are a number of links to FAQs, articles, etc. I would always start with reset-nvram and set-defaults. Apple has a good number of articles on unable to boot, troubleshooting hardware and software.