If the partitioning has been corrupted you may be able to recover the stick using this HP utility:
HP USB Disk Storage Format Tool
NB: This will wipe the stick so if you want to try some data recovery first this might help if it can see anything on the stick:
PhotoRec is file data recovery software designed to recover lost files including video, documents and archives from hard disks, CD-ROMs, and lost pictures (thus the Photo Recovery name) from digital camera memory. PhotoRec ignores the file system and goes after the underlying data, so it will still work even if your media's file system has been severely damaged or reformatted.
PhotoRec works with hard disks, CD-ROMs, memory cards (Compact Flash, Memory Stick, SecureDigital/SD, SmartMedia, Microdrive, MMC, etc.), USB memory drives, DD raw image, EnCase E01 image, etc.