I had a very similar problem about a year ago. I was on 98. I tried several different drives and eventualy gave up. I was advised by someone at work that every so often a motherboard will cause this. The only way to fix it was to buy a new motherboard. Anyway about 6 months ago I rebuilt my PC and thought I would buy a new drive (I returned my previous ones and got a refund). Everything is working perfectly now.
I'n definately not saying this is your trouble, just thought it was worth mentioning my experience.
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