Try taking your backup drive to a friend's system and see if he/she can read it. I suspect there's driver problem, not a physical degradation of the disk.
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Remembering Tyneetryk
Phaedreas Tears - 15 years old and first(*) of true neutral guilds in Atys.
(*) This statement is contested, but we are certainly the longest lasting.
<clowns | me & you | jokers>