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I have a WD external hard disk formatted as FAT32. It works perfectly on my Windows machine but when I'm trying to connect to my brand new MacBook it becomes totally invisible!

Any ideas on what can be happening?

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On Windows try to use the repair disk utilities (scandisk/defrag), do the full test and set the 'automatic repair' option before start, it will take some hours – it depends the disk size.

This is necessary because if your disk partition is damaged, OS X, to preserve the partition and your data, will leave your disk and partition untouched and unmounted until it seems to be a healthy partition.

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Does it show up at all in Disk Utility?

This is a long shot, but try leaving it plugged in for a really long time, with the Mac on and awake the whole time.

My sister-in-law complained that her year-old LaCie USB external drive (preformatted MBR/FAT32) had begun taking an inordinately long time to mount. I didn't believe her, but then watched her plug it in, and like 30 minutes later it finally mounted. After it finally mounted was a message in either /var/log/kernel.log or /var/log/system.log saying something about a date code being out of spec in the Master Boot Record (MBR).

We were able to reformat it after that (and lay down a new MBR...well actually we switched to GUID Partition Table), and it mounted quickly after that. I didn't have the presence of mind to save of copy of the faulty MBR before we paved over it, otherwise I would have submitted a bug report to Apple.

I don't recall, but I believe that the physical disk would show up in Disk Utility even before the volume out mount. Even if it doesn't, you could still try the "leave it plugged in for a long time" thing. Make sure you set Energy Saver or use a hot corner to keep the machine from sleeping.

As I said, it's a long shot, and I know it sounds completely stupid -- I wouldn't have believed it myself if I hadn't seen it with my own eyes. But hey, it's not a lot of work to try. If it does eventually mount, see if you get any interesting messages in those log files, and see if you can use some tool to copy the MBR data off the drive so you can file a good bug report.

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actually it doesn't show up on my disk utility but I will give it a shot!thanks – rabidmachine9 Jul 4 '10 at 11:28
I tried it but unfortunately it didn't you think this will change if I re-format the disk? – rabidmachine9 Jul 5 '10 at 11:49
Yeah, re-formatting the disk is the next thing I'd try. Make sure to overwrite the Master Boot Record. Come to think of it, use a GUID Partition Table (GPT) if you can. – Spiff Jul 5 '10 at 14:48
I'm sorry but how do I overwrite Master Boot Record? thanks – rabidmachine9 Jul 5 '10 at 18:05
The Master Boot Record is where the list of partitions is stored. So one way to do it would be to change the number of partitions, saving (that is, let it format it that way), then changing it back and saving again. Or just tell it you want a GUID Partition Table instead of a Master Boot Record. I would be more specific, but I usually do this from Disk Utility on Mac OS X, but that doesn't help you in your situation. – Spiff Jul 5 '10 at 19:31

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