USB flash disk missing

Question

After upgrading to Leopard from Tiger (used "Archive and Install" option), my 1 GB USB flash disk cannot be recognized by my Mac. Sometimes there is a message when I plug it in asking whether I want to format it, sometimes there's just nothing. I opened Disk Utility and can see the disk from there, tried to verify and repair it, but these options are in grey (not active). The disk worked perfectly before in both Windows and Mac. Can anyone tell me what happened and what I should do with it?
Thanks!

Answer 1

Before repairing disk permissions one should normally verify the disk first (and repair if necessary) with Disk Utility. If repairing permissions was the cause of the computer not booting it is probably due to some issue already present in the computer that repairing permissions amplified. This might also have been related to directory corruption on other drives.
The direction below are from Tiger forums but are probably the same for Leopard.
First, if at all possible make a backup of the drive in its present configuration. If something goes wrong during repair attempts and makes things worse you will have a backup. You will have to decide how to work this in the light of any present backups you may have, for example, a backup that may be a few days out of date. In that case you may want to keep that one and make a second backup of this as they are now, though I realize people often don't have a lot of empty drives sitting around.
Boot from the installer disk, select language if applicable, choose utilities, run Disk Utility and verify (and repair if necessary) the drive. You can verify a drive from DU on your main drive while booted but I have found this can result in incorrect reporting of errors. To repair your drive you have to run it from a drive other than the boot drive anyway.
Next, boot from your drive in [Safe Mode|http://docs.info.apple.com/article.html?artnum=107393] and repair permissions. You can repair permissions while booted from the installer disc but this uses the permissions configuration on the installer disc which may be out of date if you have run any updates on your computer. Booting your computer to Safe Mode restricts the number of things running on your computer while permissions are being run and does a bit of spring cleaning at the same time.
[Resolve startup issues and perform disk maintenance with Disk Utility and fsck|http://docs.info.apple.com/article.html?artnum=106214]
[Using Disk Utility in Mac OS X 10.4.3 or later|http://docs.info.apple.com/article.html?artnum=302672]
[Disk Utility's Repair Disk Permissions|http://docs.info.apple.com/article.html?artnum=25751]
From BDaqua (couldn't have said it better):
"Try Disk Utility
1. Insert the Mac OS X Install disc that came with your computer (Edit: Do not use this disc if it is not the same general version as what you have currently on your computer, e.g. use a Tiger disc for a Tiger drive, not a Panther disc), then restart the computer while holding the C key.
2. When your computer finishes starting up from the disc, choose Disk Utility from the Installer menu. (In Mac OS X 10.4 or later, you must select your language first.)
Important: Do not click Continue in the first screen of the Installer. If you do, you must restart from the disc again to access Disk Utility.
3. Click the First Aid tab.
4. Click the disclosure triangle to the left of the hard drive icon to display the names of your hard disk volumes and partitions.
5. Select your Mac OS X volume.
6. Click Repair. Disk Utility checks and repairs the disk.
Then Safe Boot, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, reboot when it completes."
If this doesn't work in repairing the computer you have a couple of options. Diskwarrior does a good job at repairing directories but costs $100. Alternatively you can do an Archive and Install.