All the HD disks are placed? If so, try to keep only the boot one (normally the first on the chain).
Also check the PSU voltage levels, specially the +5V rail. It must be on the 4.95~5.05V range, and stable!
Less than 4.95V and some circuits don't work reliably. More than 5.05 will start to fry chips inside the computer. SCSI disks are specially sensitive to this.
