iMac hardware erased but cant install os x lion 10.7
In an attempt to restore my iMac, I have managed to erase the hard drive using disk utility but when prompted to reinstall lion, it states that the iMac needs verified with Apple via the app store, but my current apple id is not working. Someone has advised that the apple id needs to be the one used when setting up the machine originally, but I cant remember it as it was year's ago (? 2010). How can I over-ride this? Also, to make matters worse, I cannot contact apple directly as the serial number has now disappeared when clicking on the apple sign on the top LHS, the only options are: start up disk, restart, shutdown, so "about this mac" has disappeared. It is not located on the outside of the machine either. TIA
iMac, Mac OS X (10.7)