So it initially works, then I used it on a Mac and unplugged it without safely removing it. Now on my Windows 7 Computer just displays a External Disk Drive and said it is not formatted.
Then I tried it on a Linux and it can display and manipulate the flash drive correctly. Is there anyway to fix my problem without re-formatting the flash drive? I don't think it would work. But SanDisk always have problems with their flash drives on my Win 7.
EDITS:
The data system is FAT32, but Windows doesn't seems to recognize. Model is: Cruzer Glide 32GB
Sometimes it would get fixed by rebooting my PC as some forum suggests, but this one wouldn't.