
im a member not an expert so this is just a comment
my flash drives disappeared acouple of months ago turns out it was the first symptoms of worms virus trogans they ended up deactivating my up to date antivirus and antispyware so they looked like they were scanning but werent. they got onto it undetected the main ones were mytob worm hellmsn virus virtumonde sci virus
so if nothing else works theres nothing wrong with a virus scan from a new free scanner/virus remover
some virus scanners/removers are in preparation guide for use before posting a hijack this log
http://www.bleepingcomputer.com/forums/topic34773.html
dont forget to change the settings to delete virus and not just scan ...

avast stinger is a good one