After I changed the BIOS Settings from "UEFI" to "Legacy" I was unable to load Windows (Error Message = "Operating system not found"). I was also unable to go into the BIOS using the usual F2 or select a boot device using F12.
I believe this was because I had turned off "Fast Start" (so when I shut down the system shut down completely), Secure Boot Manager was the first boot device in the list, and Windows 8 was installed under the UEFI settings in the BIOS and the drive was locked/protected, making the BIOS settings inaccessible. "Legacy" cannot access a Windows 8.0 protected hard drive. The odd thing is that the BIOS wasn't accessible as well (so I could change it back to UEFI).
If this happens to you, here's a 'fix' that worked to give me a bootable system and allow me to access the BIOS using F2 (and boot order using F12):
Get a copy of the BIOS updater for the BIOS on your system, or a later BIOS. I used BIOS 2.17.
I had to unpack the '.exe' installer and extract the files because the '.exe' installer didn't work.
Place the files on a USB drive.
Insert USB drive with *unpacked* BIOS 2.17 installer files
Insert USB System Recovery Drive (I used Windows 8.1 but it probably will work with a Windows 8.0 version) or Windows 8.0/8.1 Install DVD) and power on. Don't bother pressing F2 (it won't acces the BIOS).
Power on system. It will load the bootable USB drive or DVD
Go to Repair, Advanced Option, Command Prompt
Change to the USB drive containing the BIOS 2.17 *unpacked* files (> CD D: <Enter>, CD E: <Enter>, or whatever the drive letter is for the locaiton of the BIOS update files)
Type update.bat and press <Enter> (you might get a DNS error message -- no idea why)
The updater will check if the current BIOS is the same or earlier. If you have updated to a later BIOS, you'll have to use that BIOS install instead of 2.17. Go through the update process. Be sure to read ALL the instructions as you proceed.
After a reboot the BIOS will be updated and you will be prompted to shut down and restart.
After shut down remove all the USB drives/DVD
Restart and pres F2 at Acer screen (or immediately after restart)
You can now go into the BIOS Settings and change anything you need to change (be careful!). You'll see that it has defaulted back to UEFI BIOS.
Go to Exit -> Save and Exit
The system restarts and loads Windows 8.0 (I suppose it would do the same for 8.1 but I didn't test with 8.1)