Problem :
Disclaimer: I have basically no experience with BIOS, UEFI, or anything of that kind.
Earlier today I installed Ubuntu 16.04 on my Acer Aspire V5-571 alongside Windows 10. (This laptop came with 8 pre-installed, so it had the quickboot thing enabled.) After the install, both worked fine, except I’d have to go into the UEFI settings and change the boot order in order to switch between Ubuntu and Windows. This is not a very bad thing, just an extremely minor annoyance that I decided to fix by switching to BIOS. (In retrospect, I don’t see how that was supposed to help.) I went into my UEFI boot-order settings and hit the “Switch to BIOS” button. I also messed around with boot orders before that but can’t remember exactly what I did. I seem to remember there being more than one entry for Windows, strangely…
Anyway, now it won’t boot into Ubuntu or Windows, and I can’t seem to access BIOS. When I hit the power button, it gives me this message:
(there's a copyright and patent message here)
Realtek PCIe GBE Family Controller Series v2.46 (03/23/12)
PXE-E61: Media test failure, check cable
PXE-M0F: Exiting PXE ROM.
Then it gives me a blank screen with Operating System not found in the upper-left corner.
I’m fairly certain it’s not a problem with my hard drive cable, as I can access all my files from both partitions no problem after booting from my Ubuntu 16.04 USB stick.
I have an SSD, and my computer boots so fast I only see the boot “ACER” logo screen for a split second. (I had to take a video with my phone and then freeze-frame it just to figure out what key I was supposed to press to open BIOS!) I’ve tried pressing/tapping F1, F2, F8, F10, F11, F12, and Del, but none of them seem to open BIOS. Right now the only way for me to get this computer to work at all is to boot from the USB stick I installed Ubuntu from!
I assume that I need to revert to UEFI boot, but I can’t access BIOS in the conventional way. I have files I want in Windows, but not in Ubuntu.
I tried to reinstall/reset Ubuntu from the stick, but that gave me this:
The partition table format in use on your disks normally requires you to create a separate partition for boot loader code. This partition should be marked for use as a “Reserved BIOS boot area” and should be at least 1 MB in size. Note that this is not the same as a partition mounted on /boot.
If you do not go back to the partitioning menu and correct this error, boot loader installation may fail later, although it may still be possible to install the boot loader to a partition.
Hypothesis 1: Windows can boot directly to the UEFI settings from the “Restore Mode” thing WITHOUT having to hit F2 or whatever the key is. Is there an equivalent on USB-stick Ubuntu?
Solution :
Just writing an answer to summarize what helped the OP in the end (from the comments section).
Though you should be able to get into bios from tapping the F2 key repeatedly, this did not work for OP. The solution therefore is to reset the bios to default settings so that you can access it again. To do this:
1) Unplug AC power and take out the battery.
2) Figure out where the cmos battery is located on your computer. Take the computer apart until you can get to it
3) Take out/unplug the cmos battery and if possible, hold the power button down for 30 seconds. (If this is not possible, just leave the battery out for 2 minutes)
4)put the cmos battery back in, and fully reassemble the computer. BIOS settings should now be default, and you should be able to enter the BIOS again.
The correct key should be F2, try pressing it right from power on with your laptop or external keyboard. You may also get idea from this official source