Make sure the device is properly terminated, and the SCSI ID is set to an unused number. If you don't have a terminator (plugs into the other SCSI connector), have a look for a datasheet of the 40SC/Quantum HD - there may be a jumper setting that'll allow you to terminate the drive itself. I hate dealing with SCSI stuff - currently trying to get an IBM 9GB drive to work in a 20SC case ... no luck yet