USB flash drive in ExFat doesn't unmount I need to transfer large files (9 GB) from my Mac to a PC. I bought a 64 GB flash drive, and it wouldn't work because it was in FAT 32 format and I couldnt transfer such a large file. 

I reformatted the drive to ExFAT, and copied the file without a problem -- everything opened on my Mac and worked fine. When I plugged the drive into the PC, it said the drive was corrupted. So I went back to my computer, and the drive wasn't mounting. I opened Disk Utility and tried to repair it. After a while, it said it was repaired but the process never finished (even though it said in the activity log that it had been repaired). After an hour I pushed stop repair a few times, but it still didn't stop, so I just quit Disk Utility (probably not a great idea).

I decided to try starting again, and I clicked Erase in the Disk Utility so I can re-format the drive. Its now been about an hour and it hasnt moved past "unmounting disk" and the blue barber pole on the bottom.

Any ideas what I can do? Why did this happen? Should I just keep waiting? Should I quit Disk Utility? Any help or guidance would be incredibly helpful.
Force-quit Disk Utility and yank the drive. OS X will probably fuss at you; ignore it. 

Stick the drive into the Windows computer and format it there, using Disk Management. (I've had much better success with ExFAT drives formatted under Windows than under OS X.)