The problem is this: I have 3 partitions: one for backup, one for Windows 10, and the other for Windows 8.1. As I liked W10, and wanted to install Ubuntu, I formatted the 8.1 partition and installed Ubuntu there. But after that, GRUB does not work. At the time the computer is turned on, it only shows a purple screen, but without the boot options; it takes about 3 seconds and the purple screen disappears and it goes straight into Ubuntu. I have already done all the processes to install GRUB through the terminal, but it does not work (comma, it only gave me a headache to try to leave a prompt, I had to go live), I already installed Ubuntu Central, it also did not work .
Does anyone give me a light? rs