Force mount USB external HD to format?

Hi, all:

I have a surplus USB external 1TB HD that I acquired. It was formatted for use with Win7 but visible when plugged into my Yosemite Mac. I was planning to use it for Time Machine backups, but TM asked to reformat the drive (which was fine). However, reformatting failed and the drive no longer mounts on either Win or OSX environments.

I am fine with completely erasing this disk and reformatting it, but my problem is I can't get it to mount in either platform so that I can do so. The Win machine notices it when plugged in, and the USB-to-ATA bridge loads, but there is no volume associated with it. Device Manager doesn't see anything but the bridge, which it says is running fine. Disk Management sees a generic USB storage device but won't do anything with it.

Any suggestions?

Sounds like it could be a hardware problem. We need lower-level hardware information. Unfortunately you're not running Linux but Mac OS has the "diskutil list" command that could be helpful. Is there any difference in the output of that command with and without the drive plugged in?

I had a sort of similar problem once, I had to write zeroes to the drive to remove corrupted partition table information and reformat from scratch.

I can check. Right now it's plugged into the Win8 machine. Disk Management sees it (unlabeled), and says all the partitions are healthy, and says it operating normally. But the option to assign it a drive letter is grayed out, as is the option to format it. All I can do is delete the partition.

I'll try plugging it into the Mac and see what the FSCK tells me. Thanks.

OK, the Mac's terminal fsck_hfs command tells me it is partition type 0 with a small matrix of all zeros after that. It declines to do anything further.

[edit] I've gotten it to at least be visible to the Mac's diskutil, and I'm trying to format it now.

What happens if you delete all the partitions using the Win8 machine and create a new one and format it NTFS, then plug it back into the Mac?

I think you'll have to do the same low-level zero-out trick I did earlier to clear out all the traces of the old partition table that your disk formatting programs are getting hung up on.

In Linux you'd do "dd if=/dev/zero of=/dev/sdb bs=1M" where /dev/sdb is the drive you want to wipe. Within a minute the parts we're trying to erase at the beginning of the disk would be cleared and you could format again.

OK, thanks for the Linux. Right now I deleted the primary volume in Win8's Disk Management and I am reformatting it to NTFS, as recommended by szeis4 above. If that works I will try plugging it back into the Mac and re-reformatting it to HFS_extended. Thanks, guys!