Not sure.
You didn't get the prompt in command+s? bad sign.
I'd say file system corruption/bad hd.
backup asap.
You can run disk utitliy from the other machine.
Did you try safe boot? Hold down the shift key then power on.
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Start with your computer power off. Hold down command-s. Power on your computer.
Type in the following:
The first two commands will depend on your release of Mac OS X. Look at what is typed out in the console to determine the exact format.
# Type the follow two instructions to access the startup disk in read/write. Press return after each command.
# in case of partial success repeat this command until errors go away.
/sbin/fsck -fy
/sbin/mount -uw /
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Don't get your hopes up, but ocasional Apple seems to find a few discs in a back closet.
Apple may still supply the original restore CDs/DVDs for a nominal fee. Have your serial number and model information available when you call them. You do not have to be the original owner.
AppleCare Support Phone Number: 1-800-275-2273
open 6am to 6pm Pacific Time
Apple Phone Sales 1-800-692-7753
International Technical Support Numbers
http://www.apple.com/support/contact/phone_contacts.html
"You have to call Apple & likely ask for a Product Specialist to get it (Leopard), if they still have it... helps if you tell them you have a new iPhone (iPad) that needs it!"
BDAqua
10.4 & 10.5 available from Apple by calling 800-767-2775 on January 20, 2013.
https://discussions.apple.com/thread/4720126?tstart=0
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Verify/fix a disk
From your other comptuer, you can verify/fix that the filesystem on the disk is correct.
I suggest that you use disk utility to verify that your startup disk is OK.
Macintosh-HD -> Applications -> Utilities -> Disk Utility
Start up disk utility. On the left pane view, you will see a list of all your disks.
Click on your other disk.
Click on the First Aid Tab.
Click on verify/fix.
if ok, verify permissions ( not the problem for command + s )
Hopefully your disk will verify. If not, you have to boot from your installation DVD and run Disk Utility from there to attempt to repair your file-system.