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I tried to install Ubuntu 16.04 on another computer running Ubuntu 14.04 from a bootable USB stick. During the installation I chose not to delete the existing files, but only to remove Ubuntu 14.04 and install Ubuntu 16.04. I got a warning message telling me to create a partition with at least 1 Mb and a specific name (which now I don't rembember). Quite stupidly, I ignored that message and continued the installation. The installation was succesfully completed, but now I can boot from neither the USB stick nor the hard drive.
If I try to boot without the USB stick, I get
error: file not found
I tried to follow this page and I have the following situation.
grub rescue> ls
(hd0) (hd0,gpt5) (hd0,gpt4) (hd0,gpt3) (hd0,gpt2) (hd0,gpt1) (hd1)
grub rescue> set prefix=(hd0,gpt3)/boot/grub
grub rescue> set root=hd0,gpt3
because only with this choice I get a meaningful answer to
grub rescue> ls /
(in all other cases I get "error: unknown filesystem"). If I now type "insmod normal" I get
grub rescue> insmod normal
error: file not found.
Here I am stuck and don't know what to do. Note that I also tried to run insmod normal on all other partitions (as suggested here), but without success.
If I try to boot from the USB stick, I get a screen of incomprehensible messages, and I can't do anything. The last two are
[ 1.074641] Kernel Offset: disabled
[ 1.074664] ---[ end Kernel panic - not syncing: VFS: Unable to mount root fs in unknown-block(0,0)
Any help would be appreciated. PS: I don't care if I lose any data, I just want my computer to work again.