Were you using any USB hubs? I have lost 3 USB drives after using them on iBall 4-port USB hub. Initially, they started disappearing occasionally from My Computer display even though they were plugged in. Later I started to get "Delayed write failed." or some such errors because Windows failed to write properly. At this stage, the drives could be repaired if connected to the back USB port of my desktop direct instead of through the hub. That HP tool which you have mentioned above could correct the drives even when Windows itself could not format them.
After a few days, even a direct connection refused to work. Sometimes format would seemingly work, but the drive itself would not have been actually touched. After a few more days the drives became undetectable by Windows or Linux.
Strangely, one such HP 8 GB drive, has been functioning properly as a backup storage media while connected to the USB port of my router
Life is really strange !
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My experience with different local brand USB hubs has been disastrous with most of them failing to work properly. (I have tried 5 - 6 in an effort to increase the number of USB ports for my desktop.)
However a Belkin 4-port mini hub which I bought for my laptop 2 years back is functioning perfectly even today.