You didn't get the prompt in command+s? bad sign.
I'd say file system corruption/bad hd.
You can run disk utitliy from the other machine.
Did you try safe boot? Hold down the shift key then power on.
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/mount -uw /
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
"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!"
10.4 & 10.5 available from Apple by calling 800-767-2775 on January 20, 2013.
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.