If you're moving it between Mac and Windows, you want to format your flash drive with the FAT32 filesystem. It shouldn't matter whether you format it on your Mac or on a Windows machine.
To do it on the Mac, plug in the flash drive, and open Disk Utility (in your /Applications/Utilities folder). The drive should appear in the list on the left of the DU window.
Select the drive, then click the Erase tab. On that tab, select MS-DOS (FAT) as the volume format, choose a disk name if you want to, then click Erase, and wait.
That said, if your drive just 'didn't work any more' after a while, it may be faulty and it's possible that re-formatting it won't help. (All flash drives do have a finite number of read/write cycles before they don't work reliably any more, too, although it's unlikely you've reached that limit through normal usage.)
Thumb

By Jack Scicluna Photography, LLC - guest writer. The latest trend with computers is not including a CD/DVD drive. This helps the computers to be small and lighter. Apple has started doing this when the Macbook Air arrived on the scene. They have also included this with their latest laptops and their iMac’s. Recently photographers have switched from using CD/DVD’s to USB flash drives to. To format an external hard drive for Mac with Time Machine, you must follow the steps below. Step 1 Open Finder, Applications, then go to Utilities and Disk Utility. Step 2 Follow the steps above to format the drive, and then you can use it with Time Machine on your Mac system. Use Disk Utility to Format USB Flash Drive on Mac. The simplest way to format a disk in Mac OS is to simply use the Disk Utility since it is the Mac’s built in disk maintenance tool. To format USB drive on Mac using this method, all you need to do is plug in the USB device into your Mac and select it from the Disk Utility’s sidebar menu.

Format Flash Drive On Macbook Pro

Aug 23, 2008 1:22 PM