I tried unplugging the flash drive from the USB port and then plug it again, this time the error message is "You need to format the disk in drive G: before you can use it - Do you want to format it?". I tried to format it, but windows was unable to format my flash drive and error message "The disk is write protected" appears.
Luckily I found a tool to format the flash drive called "FAT32 Format". With this software you can force format your USB flash drive. Follow the steps below:
Download FAT32 Format Tool GUI (Download) (Mirror) 72KB
For Transcend users, you may use Transcend JetFlash Online Recovery
Double click to open the tool > Select a drive to format > type something in Volume label > click Start to force format your USB flash drive.
Make sure you choose the right drive before clicking the start button... :)