Ubuntu is the default OS and is installed in Legacy.
That's the problem. With Windows (almost certainly) installed in EFI/UEFI mode and Ubuntu installed in BIOS/CSM/legacy mode, there's no way for the BIOS-mode GRUB to start the EFI-mode Windows. If you followed instructions to activate BIOS/CSM/legacy support, those instructions were wrong. (There are cases when this is appropriate, but obviously not in your case.)
Change Legacy to UEFI.
That's half of the solution. You'll also need to install an EFI-mode boot loader for Linux. I'll get to that shortly. In the meantime, you must find a way to access either your firmware setup utility or your computer's built-in boot manager. I realize you say you can't access your "BIOS" (you mean the firmware setup utility; you don't have a BIOS), but you should focus on overcoming that problem. Some computers are very sensitive about the timing of keys to get into the firmware setup utility or boot manager, so you should try Esc, Del, Enter, and every function key multiple times. You might also contact Acer's technical support or post on an Acer-specific forum for help on this score. As a last-ditch effort, you can unplug your hard disk from the computer and it will probably boot into the setup utility.
If you can get into the firmware setup utility:
- Disable the CSM/legacy support.
- Disable any "fast start" option or anything with a similar name. This feature can be one reason why keypresses won't get you into the setup utility or boot manager, so disabling it can help.
- Look for other options that might affect your ability to boot into the setup utility. For instance, if one is present, you might want to activate an option to do a full USB initialization, which may get the keyboard working during boot.
The built-in boot manager lets you select between OSes, and may also have an option to start the setup utility. It should let you select between Windows and a BIOS-mode boot option that will launch GRUB and Ubuntu. You can use this to get into Windows. If you plug in an EFI-bootable USB flash drive, you should be able to boot it from this menu, too. This brings us to the next point....
Once you're able to control your boot process, you must install an EFI-mode Linux boot loader. There are a number of ways you can do this:
- Boot the Ubuntu installer in EFI mode and re-install Ubuntu. Since you've not used it for long, this may be an acceptable solution. You can verify an EFI-mode boot by looking for the
/sys/firmware/efi
directory. If it's present, you've booted in EFI mode; if it's absent, you've booted in BIOS mode.
- Boot the Ubuntu installer in EFI mode and run the Boot Repair tool. This will normally set up an EFI-mode version of GRUB.
- Disable Secure Boot, download a USB flash drive or CD-R version of my rEFInd boot manager, and prepare a boot medium with it. You should then be able to boot rEFInd, which should enable you to boot either Windows or Ubuntu. If that works, boot to Ubuntu and install the rEFInd PPA or Debian package. This will give you rEFInd, rather than GRUB, as your primary boot tool. You may be able to re-enable Secure Boot at this point, but that's optional.
sudo update-grub
?