Unfortunately, USB flash drives are not a failsafe way to store data. Because they are so portable, they are exposed to and can be affected by many outside conditions. A flash drive can loose partition information and/or lose data by it being exposed to strong magnetic fields, static charges, shock, water, extreme heat, extreme cold, and other factors including (many believe) x-ray exposure. In some cases, data loss can be attributed to poor design and circuitry in the memory stick itself.
Now... what to do when you can no longer access data on a memory stick...
First of all, DO NOT reformat the drive. This will most likely overwrite existing files making them un-recoverable. Also do not add any more files to the drive for the same reason. Set the drive aside and then install a data recovery program to your computer.
There are plenty of excellent data recovery programs available that will work for USB drives. However, you may have to try several to see which one works the best.
(by your post, it sounds like you may have already reformatted your drive. Don't give up. I would still try a few recovery tools to see if they can salvage anything)
Here are some freeware options:
Smart Data Recovery:
http://tinyurl.com/2kcsmm
This one worked for me a few times. They also have a version for U3 Flash Drives.
SoftPerfect File Recovery:
http://tinyurl.com/jcacz
ADRC Data Recovery Software Tools:
http://tinyurl.com/ppdn9
Here are some more extensive shareware options that have free trial versions:
Pen Drive Data Doctor Recovery:
http://tinyurl.com/2yak98
BadCopy Pro:
http://tinyurl.com/ynsv8n
Key Drive Recovery Tool:
http://tinyurl.com/2s6x24
Data Recovery 4 Pen Drive:
http://tinyurl.com/39t2vx
If all else fails, here are two companies that specializes in data recovery from memory sticks:
http://tinyurl.com/2nlfa3
http://tinyurl.com/38krc4
Please let me know if this helps.
Good Luck.
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