Help - unfamiliar screen appears instead of GRUB

Instead of the purple GRUB screen, everything I see when I try to boot is this. How to fix this?

Edit: Yes, I have multiple partitions. I recently tried to expand the size of the partition in which Ubuntu is installed (using GParted), but I cancelled the operation in the middle of the process because it was taking too long. When I tried to log in again, a message of error appeared. I then searched the web for a solution and I found a couple of terminal commands to reinstall GRUB. The result was this same screen below.