Try this, from the Symbianize forum:
So, with nothing to lose, I pasted
http://u3.sandisk.com/download/lp_installer.asp?custom=1.6.1.2&brand=PelicanBFG
into Internet Explorer, thinking that it would at least get me some
new files that might allow me to reformat the drive. I followed a few
prompts and lo, the U3 Launchpad Installer software launched and
restored the drive to its factory settings of 2 GB capacity formatted
as FAT. It even replaced the original U3 files, making it truly
good-as-new.
I’m astonished that this information isn’t more widely available,
particularly on the SanDisk support site and forums, as this 0
capacity problem seems to affect a good number of drives and there are
many threads where this issue remains unresolved.
Note that the page at
http://u3.sandisk.com/download/lp_installer.asp?custom=1.6.1.2&brand=PelicanBFG
requires you to install an ActiveX component, so you must use Internet
Explorer.
Otherwise, you can download the latest version of the U3 Launchpad
Installer executable from the Sandisk KB.
Of course, if you’re not using a SanDisk drive, it’s rather unlikely
that this software will fix your drive, but maybe your device’s
manufacturer has something similar. There are also a number of good
ideas in the comments below, so definitely read through them for more
options.
If you’re trying to restore the drive’s contents or recover files, the
all of the methods described on this page will format (erase) the
drive and are not for you. Good luck.