The first thing to say is that termination of the scsi bus would need to be done on the internal drive itself, rather than externally on the back of the machine. Some of these older drives were terminated automatically, while on others there is a jumper that needs to be installed on pins generally marked TE. It is possible that the drive has failed, but it sounds to me more like you have not got the termination right. That would be the place to start.

The second thing is to ask whether the new drive installed was Apple-branded (basically, does it have an Apple logo on it)? The default installer will not work with a drive that does not have Apple ROMS (though there are workarounds).

Let us know and we can talk you through the process.