how to recover my built in win10 when all files are gone - Microsoft Community

i bought aspire v15 - v3-574g-77p6  8gb/nvidia940m 4gb/ win10  around year , half ago. 

while playing, laptop crashed , when restarted, diagnostic tools kicked in. tried recover no luck, last resort resetting may laptop, did, after booting, stops around 55% hang. try restart, not successful.

went acer service center, acer said needs replace motherboard 700usd, buying laptop. still looking solutions.

in mind, think built in win10 got corrupted or something, maybe can use windows 7 reformat laptop (by way, missed doing recovery files on usb.) because have cd of it.

my question is, how can retrieve licensed win10 built in (license number) can download win 10 , provide existing license, in case installation of lower version successful.

thanks

edward

well edward if installed same version (home, pro . . .etc) should automatically activate when system on web

have tried going settings app - update , security - activation , clicking activate now

failing that, try page troubleshoot activation issues, if none of solutions work, click 1 of 'customer support' links on page

Windows / Windows 10 / Windows update, recovery, & backup / PC