Can't format or use internal hard drive
I have a 2007 MacBook that was running 10.6.8 on a replacement HD (500 GB). I've gotten a new MB Air and want to wipe the HD and reinstall the system so my kids can use the old MB. The MacBook was working fine when I started this process. When I booted with the original install disk and selected Disk Utility to erase the drive, Erase failed with an "input/output error." I can't format the drive and I can't even select the drive to re-install without erasing the drive (no drive shows up in the installer). This is happening whenever I try it now.
Now I can't even use the HD to boot the MacBook. Disk Utility can see the drive but it shows up as a 3.6TB drive, not a 500GB drive, and it's only one line in the sidebar (usually there are two lines per drive). Info is backed up so I don't care if I lose everything, but I'd like to be able to use the drive as this needs to be a low budget computer. Partitioning does nothing, all attempts to erase it fail. Next step is probably to remove it and try to erase it in an external enclosure.
Can anyone explain what might be going on? Why would the drive suddenly stop working to the point of not even being properly recognized when minutes before it worked fine? And what can I do about it?
Thanks.