The IDE controller on the PowerEdge 1300 was only validated with the CDrom, hard drives have not been tested.
Did you set the Scsi ID for the new drive? Each Scsi hard drive must have a unique ID, set by a jumper on the hard drive. Hard drives are usually the lower numbers, but you can use any number except 7, which is the controller. This is an example of the jumper settings:http://docs.us.dell.com/docs/storage/2731c/Jumpers.htm
Are you sure the Seagate part number is ST118202LC? This is an 80 pin hard drive, not designed for the PowerEdge 1300. The 1300 should use 68 pin hard drives.
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