hard drive

I have 3 dimension 8100 and 1 440 towers. The 4400 was and is functioning. The 3 8100s I rebuilt from my pile of parts. I only had 2 hard drives, a 40 and an 80, both WESTERN DIGITAL. Neither drive was "FOUND" in any tower. I ordered 5 more WD 80s from EBAY, 2 sellers. Apparently THAT hard drive was also bad as it too was "NOT FOUND". At least this eliminated the towers as the culprit. The second batch of 4 came today. I installed one in the 4400. It was set to CABLE SELECT. I left it that way. It was detected, activated, and the OS reload was successful. The 8100s are next. I guess the moral is that nothing can be taken for granted.