OS X 10.6 Snow Leopard no longer mounting an external USB drive

OS X 10.6 Snow Leopard no longer mounting an external USB drive I have a 1TB generic external hard drive containing a single HFS partition. I originally formatted this using Disk Utility and it worked fine. Now, for some reason, it's not auto-mounting when I start up.
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Total answers/comments: 2

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Guest [Entry]

"It looks like the problem was the partition table.

$ diskutil list
/dev/disk0 # The internal hard disk
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *500.1 GB disk0
1: EFI 209.7 MB disk0s1
2: Apple_HFS Macintosh HD 402.5 GB disk0s2
3: Microsoft Basic Data Boot Camp 97.1 GB disk0s3
/dev/disk3 # The external USB drive
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *1.0 TB disk3
1: EFI 209.7 MB disk3s1
2: Microsoft Basic Data 999.9 GB disk3s2
# ^-- Hey, that's not right!

The filesystem was intact, but the HFS+ partition on the external drive was mistakenly flagged as Microsoft Basic Data instead of Apple_HFS. I used the GPT fdisk utility to change its type back to HFS+, and it immediately appeared on the desktop and worked normally again."

Guest [Entry]

A post at Apple Support forums indicates that DiskWarrior might help you in this scenario.