I was using my laptop last week when the rainbow wheel appeared. Whole system froze up so I did a force shut down, shrugged it off and went to bed. Next day I tried to boot up and after a few minutes of the apple logo and the waiting circle, I got a prohibitory sign (circle with a line through it). Looked around, found no help. Option-s start: would tell me it was "still waiting for root device" and that was it. Reset nvram and pram, no help. Took it in to the Genius Bar where I was told it was a dying hard drive. Tried to backup the data onto my external while still in the store (not sure how he was getting access to it as I could not start up myself) but it would freeze up after a few gb. Went home and used a friends macbook pro to go into target disk mode. All the data was retrieved without a single problem. Now I just got myself a new HDD (320GB 2.5" Hitachi Travelstar Z5K500 5400RPM 3.0Gb-s SATA 7mm Notebook Drive 8MB) to replace the supposedly failing stock one. I installed it correctly, but the problem is that 1) It doesn't show up when I hold option on startup, and 2) When booting from the (snow leopard) install disc it does not show my hdd as an available disc to install on. I have tried using disk utility when booting from the install disc. The drive shows up but the "untitled" parition inside it is grayed out. I was told the solution was to format it. When I try to format (zero out, 7 pass, etc.) I am given an error telling me it "Cannot allocate memory". So I removed the drive and plugged it in with a sata/usb cable as if it were an external. I was able to format it this way so I placed it back inside the laptop. Still the same problem. Installer not showing the hdd as an option. I've read that others with similar problems may have had a failing hard drive cable, but wouldn't my hdd fail to show up in disk utility if that were the case? I have been without this laptop for a week and have yet to fix this issue. I am becoming increasingly annoyed, saddened, and desperate, as this is my only personal computer. I am hoping that someone here can be of a little assistance with this issue. Thanks.