The Acer Aspire One has a built-in BIOS recovery routine, making it possible to flash the BIOS even if the system doesn't boot anymore. It's only meant for emergencies and may void your warranty, so use at your own risk.
1. First format an USB stick with FAT.
Download the latest BIOS, and put both FLASHIT.EXE and the BIOS file in the root directory of the stick. Rename the BIOS file to ZG5IA32.FD, that's important. Do not remove the USB stick.
2. Turn the Acer Aspire One off, make sure both battery and AC adapter are connected. Press Fn+Esc, keep it pressed and press the power button to turn the AA1 on. Release Fn+Esc after a few seconds, the power button will be blinking. Press the power button once. The AA1 will now initiate the BIOS flash, do not interrupt it under any circumstances. After a while the power button will stop blinking, and the AA1 will reboot shortly after.
3.The BIOS has been flashed and all settings reset to default.
If for some reason you made a mistake during the procedure and it doesn't reboot by itself wait 5 minutes before turning it off, just to be safe that it isn't still flashing the BIOS.