I have a 1st generation Macbook laptop. I swapped out the original 80GB HD & installed a larger 320GB internal HD I recently bought on Ebay. At 1st, everything seemed ok, the hard drive mounted ok and I went ahead and proceeded to 1st partition the drive into 4 80GB separate partitions, with a plan to install Snow Leopard on one of the partitions, have 1 for room for a backup drive, and the other 2 partitions would host Windows 7 & possibly Linux, via (bootcamp). After experiencing some frustration with the installation of Snow Leopard, it appeared everything was ok, so then I went ahead and migrated my entire original 80GB mac factory HD over into 1 of my partitions. Everything seemed to go quite smoothly up to this point. However, soon afterwards, my HD somehow was no longer mounting! It still has not mounted ever since this time. I have tried taking the HD out and swapping it with the old one and it still will not mount. However, the original hard drive mounts right away without any issues. My entire livelihood is essentially thru my computer as an online grad student, so I went out to Frys Electronics & purchased a WD Scorpion Blue 500 GB HD after experiencing all of these issues. The new HD is working flawlessly. However, my issue and question is, what can anyone with technical knowledge suggest I do to completely erase the other non-mounting HD? I plan to send the non-mounting HD back for reimbursement to the Ebay seller soon. I'm concerned because, as I previously mentioned up above, this HD still potentially is holding all of my personal information from my previous drive I had for years installed into the macbook. I have searched far and wide online for any answers to this issue and would appreciate any help in this matter. Please help, Mac Techies!!!! Please help this learning Mac Techie JR & sorry for the long post, but I feel like it's better to get out all of the info 1st, right away!!!!