Alright I think you are experiencing a problem that I had with time machine; just for curiosity what hard drive are you using? I am using Mybook, but I think this should help anyways. Before you do anything i would make sure the computer reads the drive, like when you plug it in, does something come up? If not then go to disk utility and format it to FAT after this everything should work fine. Now open up the disk utility and click on the partitions tab, once there create two partitions but make sure you click on the options thing and make them both GUID, also be sure it read Mac OS Extended (Journal). Once those partitions are created go back and revert the process (Make it one partition) name it whatever you wish but keep the GUID setting and the os extended journaled. Now everything should work flawlessly. You shouldn't have any time machine problems. I do recommend having two partitions that way time machine is not taking up your entire external drive, because it will use it all up if you have 1 partition. When I first got used time machine I let it use a 750 Gig drive; I had this as my main storage unit and would place movies and other non mac related documents in there, after a while I noticed that some of my stuff was vanishing like some messed up prank my computer was pulling on me, but no, time machine just deleted stuff you put on your drive to make room for backups, so once again don’t make my mistake make two partitions.
