Need to wipe out HD but don't have install disk? I have lion 10.7.5

Reinstall your computer with Snow Leopard - original disk- and it is ready for resell.

You cannot resell your Lion OS as it is under your Apple ID and you cannot resell it.

First, if you purchased Lion at the app store, the license is not transferable - it is forever tied to your Apple ID. So you can't sell the machine with Lion on it (there is no install disk for Lion anyway). You do need to reinstall the original OS so the buyer can purchase Lion with their own Apple ID.

As for your problem with the install disk - you do need to boot from another disk in order to erase your hard drive. Have you tried to insert it and then go to System Preferences > Startup Disk > select it and then hit restart?

1. Make backup - if you need it.

2. restart computer with C key held and Leopard OS in optical drive

http://support.apple.com/kb/HT1544

After you boot from the disk and immediately after the installer goes through the language selection, you will see Utilities in the menu bar. Go to Disk Utility, choose your internal drive, and hit erase (for safety sake, I'd suggest doing a 3x pass of writing zeroes - find it under Options); when the erasing is finished (be prepared to wait for several hours depending on the size of your drive), then it will automatically reinstall the OS.

once you erased the drive as babowa mentioned and started the install you can leave it for approx 1 hr - or longer if you wish - it will install itself.

I see you got your question answered - when the erase is done, you do need to click on install (if I remember correctly - haven't used a disk in quite a while). After that, it's automatic.