How to get my lost preinstalled windows 8 product key?

You should have a separate form of information like a sticker with the code on it or the code on a label that was with all the information you got when you purchased the laptop

Did you look for the product key on the bottom of the system? Sometimes it's under the battery.

You can find the license key easily. All computer makers put a sticker on the computers they produce that shows what operating system is installed and the license key. On laptops the sticker is on the bottom of your laptop so you just need to turn it over and copy the information onto a notepad so you can use when you reinstall Windows 8.

If you need assistance reinstalling Windows 8 you should contact Lenovo support. They can advise you on your options for reinstalling Windows 8 - http://support.lenovo.com/...ok?TabName

As well as those places to look, when your Win8 was activated, its product key was recorded at Micro$oft. Check with them.

If you happen to have Windows 8 still on your laptop like on another partition, you can download a free copy of Belarc's Advisor and run it and it will display your product key and other passwords.

http://www.belarc.com/...elarc.com/

If you deleted Windows 8 entirely, then you would need your printed material to find your product key. Try also looking at the bottom of the laptop to see if there's a sticker there with that information.

Your Windows 8 Product Key should be on a sticker affixed to a label inside the battery cover.

Do you still have you lenovo windows 8 media disk? If you don't call support have them send you a copy?
Next install only with the lenovo disk, The disk will detect the SN of the motherboard and install windows, no need to look for the product key. Lenovo Dell and HP tie their windows product key to SN that is if you have the right media for that model.

Aren't you glad you brought Lenovo! Enjoy