Yeah, the drive mappings can get confused, even on your own system, so throwing it on another just leads to chaos! i.e. Assign the drive the next free drive letter... yours might be F:\ mine is I:\

Could have been a retro-virus (mutil-headed hydra - lol)... but like the old days of Floppy's, they infect the boot sector of the USB drive, and infect/corrupt/transfer when plugged in... I never share my 'important' usb stick.

I'd say if you ran the chkdsk/HDDregen/etc, and still not fixed, then it's toasted. Do a low level format and hope for no new bad blocks.