How can I restore my PSP to factory after a failed firmware update without sending it back to the factory?

your best bet is to buy or make a Pandora's battery...only if you have the PSP 1000 or 2000 series...not the new PSP 3000, and once you get the Pandora's battery, if you bought it make sure you buy the magic memory stick. this will also get you custom firmware and allow you to download backup copies of your games to your PSP. making them isn't to hard but you'll need to buy another battery anyways and the Pandora's batteries are cheaper than regular batteries. so it's well worth it...also check out mikehacks.com, PSP-hacks.com, PSPslimhacks.com to see what you can do with custom firmware and how to unbrick your PSP...good luck