grubrescue – How can I boot from a usb key when all I can get is a Ubuntu grub rescue prompt?

My Acer Aspire One D270-1596 boots to a grub rescue prompt.
I’ve been able to set root and prefix to get to the Ubuntu 18.04 grub (?) page and memory test menu, but running Ubuntu or a restore version fails to find /root/dev and says target filesystem doesn’t have requested /sbin/init.

Typing “ls” at grub rescue> gives me HD0 partitions called hd0,msdos6, 5, 3, 2 and 1.

Typing “set” from grub rescue> tells me:

Typing ls (hd0,msdos7) tells me “error: no such partition”

Typing ls (hd0,msdos5 or 6) tells me both Filesystems 5 and 6 are ext2.
All other partitions say “Filesystem is unknown”

Setting the prefix=(hd0,msdos5)/boot/grub and root=(hd0,msdos5) then insmod normal and normal get me to the Ubuntu grub menu.

Doing this for (hd0,msdos6) tells me “error: /boot/grub/i386-pc/normal.mod not found”.
Doing it for (hd0,msdos7) says there is no such partition, even though (hd0,msdos7) is presented using the “set” command.

Choosing “Ubuntu” or other versions in the GRUB menu on (hd0,msdos5) says “mounting /dev on /root/dev failed: No such file or directory” and takes me to BusyBox v1.21.1 and a prompt (initramfs) where “help” gives me a long list of commands that mean nothing to me.

I have a bootable USB key for Ubuntu 18.04 which I used to install Unbuntu on another computer. (The one I’m using now to try to recover my Acer.)

It shows up as (hd1) at “ls” at grub rescue> if plugged into the Acer, with one partition, (hd1,msdos2)
The (hd1,msdos2) partition shows as an unknown file system.

Pressing F2 (or F12 or F10) while booting the Acer does not take me to the BIOS menu so I could boot from the USB key.
This seems to me to be the most straightforward way to resolve this problem. Can anyone recommend a way to get to the BIOS menu since the built in prssing of F2 doesn’t work?

This is (was!) a perfectly good computer with 2 GB of RAM and a 360 GB hard drive that I would like to recover even if I might lose what’s on the hard drive already.

Can anyone help me?

Bob Thomson
Ottawa Canada