I Just thought of something for you. A friend of mine brought his power book over for me to transfer a files I had stored in one of my external drives. My drive icon appeared on his desktop but I couldn't drag n drop the file over to his computer. It just didn't work? Now all my computers are running the lastest Tiger updates, 10.4.10 and the powerbook was running 10.4 only.

I ran repair permissions on his computer, it corrected a few items but still it didn't work so I used his Tiger disk to do a new install with the custom option "save previous system folder" and installed whole new system on the powerbook. Than I installed all the software updates to 10.4.10. and restart the powerbook.

I ran repair permissions and attached my firewire drive to the powerbook. I drag n dropped all the files from my drive to his without any problems.

PS: When you are formating the external drive using Disk Utility, make sure you format in "Mac OS Extended (Journaled) and click on the Partition section using 1 partition or several partitions. Then click partition to format.

Well I would not call myself an expert in this field but for a emergency solution that is effective but not cheap, I would use Alsoft DiskWarrior for the task. That would find the disk and mount it, run it from the machine where the disk is not mounting.

You may have to format it for a Mac. Did it come with any software? If not go the manufacturers web site and see if the HD is formatted for a MAC and if they have a software download for it. All HD's do not automatically show up on a MAC. You can format a HD by using the Disk Utility in the Utilities on the HD but if it is not showing up there you cannot do it. Take a look there as it could be showing up as a HD that you can format. If it shows up format it "Mac OS Extended Journaled". Once you are at the disk utility folder go to the erase tab and you can select which format to use as you erase the HD>