We bought brand new the Aspire Acer Es1-520.  It came I believe with windows 8 (as acer explorer is on the computer and I believe that was from Win 8?) but the people at Fry's convinced my husband to install Win 10 on the computer before it left the store.  (GRRRRR)  Over the course of the next months we tried to use the computer and it ran at 100% cpu and 100% disk  and high memory (can't remember the number).  The cursor would jump around and loading anything was impossible. It would take over 10 minutes sometimes for each action to happen. My husband got frustrated after Fry's said there was nothing they could do but reset Win 10, and he threw the computer in the closet.  Now well out of warranty, I am trying to get this brand new computer to run.  I did a factory restore and conveniently it only says Win 10 can be found, what happen to the Win 8?  I believe Fry's must have deleted it.  I also have tried to disable everything and anything that is running from xbox to onedrive.   I hate Win 10 and I would love to never have a computer with it on, however, my daughter needs a computer for college and this one is brand new and I would like to get Win 10 working. 

My questions are:
 I have a Wins 7 disk that is from a dell computer can I use that product key to download to a USB drive and then put it on the Acer computer?   
After disabling and getting rid of many apps the CPU and disk usage does drop and now in idle run better; however, when we go to use any programs or after startup and randomly sometimes when sitting idle they do spike up to over 80% usage and the lag makes it almost impossible to use. What else can I do?
Can I disable this Cortana?  
Was this Acer ever designed to really run Win 10 since I believe it came with Win 8?

I have some computer abilities and am willing to try what needs to be done to get this computer to work.  I am sorry for the confusing post. 

Thanks for the help!
Desperate and frustrated
Annie