The drive is dying, that's what your problem is. You'll need to take it somewhere, and if they're very kind, they will stick the bad drive into a device to see if they can coax it into letting you get the last of your data off, but at this point it sounds like it may be too late.
My 27" iMac is freaking out. It suddenly won't recognize the system on the internal hard drive, but only sporadically. It will display the flashing question mark folder, so I'll start it with the system disk. When I try to switch the startup disk, the internal hard drive doesn't appear. In Disk Utility, the internal hard drive appears as a disk named "Media", and my only option is to format it. After unplugging the iMac for a period of time, it will come back and start up normally--until today. Today, it hasn't started up normally at all. I installed 10.6 on an external hard drive, booted up, and was met with the, "This disk cannot be recognized blah blah blah" message.
My iMac is long overdue for a total reformat and reinstall, and I've been slowly backing up files (hundreds of GB of video projects). Unfortunately, I have a few important files left that I really need to rescue, or I would just format now.
Any ideas why my "Macintosh HD" would suddenly and inexplicably become unreadable "Media"? Any ideas of what I can do to at least rescue my last few files?
Mac OS X 10.6.4
iMac 3.06 GHz Intel Core 2 Duo
4 GB RAM
500 MB hard drive
Attached peripherals: Wacom tablet & WD My Book dual 500 GB RAID drive