The machine in question:
Windows XP Pro SP 2
AMD Opteron 175 (dual core)
MB is an A8N-SLI Deluxe
2 GB RAM
system drive is SATA
media drive is 2xSATA in RAID 0 (but I don't remember if I'm on the NVidia or the Silicon Image controller)

I was told the machine was unstable and slow, then there was a problem with the RAID array. When I examined the PC, drive manager reported the array as Healthy (At Risk). Some files (roughly 20%?) on the drive are listed with correct file data but are unable to be opened. When the system is being dodgy, processor utilization is listed in task manager at 50%+, but system idle process is still in the 90s, which I thought was impossible.

As I'm attempting to repair or scan the disk, the system becomes unstable. Part of the way through the scan it will lock up. 10 minutes later CPU usage drops to 50% and still no progress. Eventually I get an error: "Windows was unable to complete the disk check."

Does replacing the RAID drives make the most sense, or is this likely a controller or different problem? And is there a diagnostic test to get a handle on what's wrong and how much data is lost? There doesn't appear to be a diagnostic option in the controller menu that comes up after POST.