Reinstalling Mac OS X Lion

Given the age of your equipment, if you have firewire then yes, you will need a cable. Also, just FYI, if you have an external drive you can hook up to your parents computer you can install Lion on it just by selecting it when you go to install. When done you can hook it up to your mac by USB. Then when booting up hold down the OPTION key. After your mac does its self check it will reveal your 'start up' drive options. You should then see your external drive. Click on it and your mac will now run off that new drive, just not quite as quick as it usually runs. Once you are up on that drive open DU again and try to repair-partition-restore your original drive before you give up. After you have managed to recover your original HD when you go to boot up on it you should reset the pram by holding down the shift-option-command-r keys all at the same time. You can manage this with your right hand if you try; then hit the start button with your left. You will hear your mac chime and you KEEP HOLDING the keys down. As soon as you hear a second chime release all four keys and let it boot up. This will prime it for the new osx you'll install once you get back to the rescue/recover window OR just download it LION again to your external drive and use it to select your computer for install once you get your hardd rive to show up. This is a lot of info and Im not going to be online for awhile. Just take your time and go through it slowly. Personally I like the external drive option, but if you don't have one that can be spendy too. Good luck.

Darn, I messed up the command for the PRAM reset. The four keys are the Option, Command, P, and R keys. Everything else is good.

Apple quit supporting Lion 10.7 around 2009 I think. You're lucky to get your hands on it. It sounds like you have corrupted the master boot file on your hard drive. Judging by the age of your computer you may need to do a "Target" boot up onto another computer (perhaps your parent's). You can find information for doing that. If you are successful open up Disk Utility on the useable Mac and have it look for your computer's HD. If it still shows it grayed out that means it can't recognize the boot up block most likely. On Disk Utility (DU) there is a "Mount" option. If clicking on that doesn't do anything then click on first aid and try to repair it. If that fails try again to partition it. If you get that far change it to 2 partitions (you don't really have to name it at this point). This "OVER" writes the master boot block on your hd. When thats done click on it again and tell it to make a single drive out of it and this time NAME the drive "Macintosh HD". You should then be able to move forward. If any of this helps and you can now see your hd then open your browser (on your parents computer) and try to download Lion again (to your parents computer) while still in Target mode with yours. When the download completes click on it and start up the program. When it opens you will be asked which drive you want to install Lion on. Select your computer's hd and then follow the instructions. Average install is around 45 min if I recall. If none of this works you may have to either take it to a tech who can overcome it. I could if I had it here but thats not possible. A true tech can fix that. Also, you may want to just buy a new hard drive and update your Mac. There are many websites that will show you how to do that if you google it. May 'the force' be with you! Good luck.

I would only be cautious that both of your macs have firewire 800 ports. If this is so then yes this is the right cable. But if either one of your machines has a firewire 400 port then the cable would not work. Just FYI there is a site where you may benefit from should this not work and you need to replace the hard drive to overcome it: Repair Manuals for Every Thing - iFixit - good luck.