I'm trying to convert the FAT32 file system of an external hard drive to NTFS. Here's what happened:

C:\Windows\system32>chkdsk G:
The type of the file system is FAT32.
Volume PIETEREXT created 3/19/2008 12:43
Volume Serial Number is 1806-2E30
Windows is verifying files and folders...
File and folder verification is complete.

Windows has scanned the file system and found no problems.
No further action is required.
  488,264,768 KB total disk space.
       72,192 KB in 1,503 hidden files.
    1,281,792 KB in 40,029 folders.
  309,235,168 KB in 199,915 files.
  177,675,584 KB are available.

       32,768 bytes in each allocation unit.
   15,258,274 total allocation units on disk.
    5,552,362 allocation units available on disk.

C:\Windows\system32>cd \

C:\>convert g: /fs:ntfs
The type of the file system is FAT32.
Enter current volume label for drive G: PIETEREXT
Volume PIETEREXT created 3/19/2008 12:43
Volume Serial Number is 1806-2E30
Windows is verifying files and folders...
File and folder verification is complete.

Windows has scanned the file system and found no problems.
No further action is required.
  488,264,768 KB total disk space.
       72,192 KB in 1,503 hidden files.
    1,281,792 KB in 40,029 folders.
  309,235,168 KB in 199,915 files.
  177,675,584 KB are available.

       32,768 bytes in each allocation unit.
   15,258,274 total allocation units on disk.
    5,552,362 allocation units available on disk.

Determining disk space required for file system conversion...
Total disk space:              488384001 KB
Free space on volume:          177675584 KB
Space required for conversion:   975155 KB
Converting file system
The conversion failed.
G: was not converted to NTFS

I looked at the TechNet page for my error, but after closing every app the conversion was still failing halfway through. Why does it keep failing? I kept an eye on Task Manager but it didn't look like my system resources were near depletion. I'm using Windows 8.