I have a 2011 Macbook Pro 15 inch, 8GB RAM, with self-installed SSD and HDD inside, running Snow Leopard. It has worked like a charm since day one. It's been nothing but great. Yesterday, one of my LaCie Rugged 500GB external hard drives wouldn't mount. Just didn't show on the desktop. So I tried my OTHER LaCie Rugged 500GB (same type) external hard drive, and it wouldn't mount either. So I plugged in an older Seagate hard drive, and that mounted just fine. So I checked on my Mac Pro (latest version, 24 GB RAM, 2TB internal hard drive from apple, running LION) that I have at work, and all those drives mount just fine on that one. So it seems that my LaCie hard drives are fine (i.e. not failing?), but just will not mount on my Macbook Pro. I've been using these for months with no problems. So what could be the problem now??? I've looked at many similar posts, but my problem seems different. The hard drives don't seem to be failing because they work just fine on my other mac. But on my laptop only these two have stopped mounting...and at the same time (same date). One idea: recently there was an Macbook Pro EFI update...could that have caused the incompatibility? Anyway, I'm baffled, and if you are so kind to have read this far AND can offer some help or advice, I thank you in advance. Additional info for those kind enough to have read this far: The LaCie Drives each have three partitions: Mac OS Extended Journaled (234 GB), NTFS (234 GB), FAT32 (32 GB). The Seagate is 1 TB of FAT 32 (I know, you're not supposed to do that, but I didn't know what I was doing when I formatted it, and amazingly to me, it works just fine!) None of the partitions on any of the hard drives mentioned are even half-way full (including my internals). They don't mount on my desktop, and they don't show up anywhere else on the Finder (but everything else does). Disk Utility does not see them. EDIT: forgot to add, I do hear the hard drives spin when I connect them to my Macbook Pro. Spinning sound is regular, steady, like normal.