My original system is Windows 8.1 Single Language.Last day i'am careless clean up the computer disk.My computer is no OS already and then I'am install back windows 10 Technical preview.
I don't how to download back my windows 8.1. Because my acer laptop back no windows 8 product key.

You can download the Windows 8.1 install files here: http://windows.microsoft.com/en-US/windows-8/create-reset-refresh-media

But if you don't have your Windows 8.1 key anymore, you'll have to call Acer Support or dealer you bought the computer from and tell them you lost th

Hi,

Note: Since OEM product key usually binds to your motherboard model, if your laptop come with OEM Windows system and you lost it, Windows installation media created by media creation tool cannot be activated by OEM key. You might need contact Acer for recovery disk or read your user manual for more information of your system for recovery assistance.

Regards

D. Wu