sounds like it got corrupted somehow, try eddie B`s suggestion, if that fails then it may be dead, I never heard of a pendrive dying myself, but my brothers kids managed to kill a cheap MP3 player by yanking it out before it had finished transfering, just couldn`t do anything with it after that, you could see if there are any pendrive tools out there on the net.
Mentor.
PC1:XP, P4 3ghz, 1gig mem, 3x160gig hd`s, Radeon 9800pro, 6 way sound.
PC2: Linux, AMD 2ghz, 512mb ram, Nvidia GeForce4mx, 16 bit SB.
PC3: XP, laptop, intel 2.6ghz celeron, ATI 9000igp, 256mb