If you burned recovery disks when you got your computer (every OEM computer I know of recommends it within the first 30 days) then just install those. Or you can also contact Acer & they should be able to sell you the specific recovery Disk(s) for a significant fee, normally around $100.
Is there a label on the computer with a product key? You don't have other options without a valid product key.
If you have the product key then your third option is a Win 7 ISO...
Finding the Windows 7 ISO is difficult now but it's still around if you look hard enough, you probably need the 32 bit version but get whichever you had . Then you need software like PowerISO to edit the ISO file & delete the ei.cfg file. Now install & choose the Home version. Put in your product key.
And go to the Acer website to download any missing drivers.