Hard drive not mounting

My Macbook Pro was running absolutely fine until I tried transferring a 10GB file from an external disk drive. It froze 3 times and each time I had to switch the power off on my machine to restart (it's at this point I gave up trying to transfer but I wish I'd given up earlier!)

Shortly after my machine started freezing, and after this happening about 3 times my machine won't get past the grey apple logo/spinning wheel.

I've tried booting from my Snow Leopard CD and Disk Utility found no problems, so I decided to try reinstalling Snow Leopard - it began working and then stopped, saying it couldn't install and no longer showing my hard disk. Since then I can't get the hard disk to show as a disk in Disk Utility...

Any ideas? Any help much appreciated.

I can hear the disk spinning as it tries to boot but it's still just sitting on the grey apple logo screen...

It sounds like the drive may be failing or has failed. I am not sure if this will work but you can try the following:
1. Turn the power on on your Mac.
2. Immediately after the startup chime (bong) press the command and s keys simultaneously.
3. A text screen will start scrolling. When it stops tip fsck -fy and press enter.

Your Mac will check the hard drive similar to they way it did in Disk Utility. If it reports the volume is OK try to reboot the Mac. If errors are reported that were not repaired try running the fsck command again.

Thanks - tried that and it said the disk was fine, I then tried to exit and it came up with an error and then suddenly came up with lots of lines repeated:

disk0s2: media is not present.

Restarted and tried again and said "Root device is mounted read-only" then after that "the volume appears to be OK"

After I try to exit it comes up with "Cannot get audit control port. Warning: audit system low <5% free" (there's about 10GB space left on my hard drive)

Then it comes back with diskos2: media is not present again...

I've tried reinstalling OSX again from the CD and the same thing has happened - it starts installing and when it gets to about 20% it says it doesn't have enough memory, then shows what it's trying to install on and it's the below - the hard drive seems to have vanished after showing before...screengrab attached.

Apologies for bumping this but the issue is still happening - it seemed like it was better for a while but now it's back to crashing all the time...any ideas?

Even though the file system check stated the hard drive is OK, I suspect the drive may be failing. The file system check, both the command line version and the Disk Utility version, can only check the integrity of the file and folder system. It does not check the hardware or drive electronics.

You may have to replace the drive.