Ubuntu 20 boot blocked, loading initial ramdisk

I have just installed Ubuntu 20 Mate. When I try to boot it, the process is blocked at loading initial ramdisk. I already tried to reinstall it. What could be the problem? I am using a Dell Inspiron 15 5567 with Intel i7-9700U, 16Gb RAM, AMD R7 M445 dedicated GPU. These are my partitions: Disk /dev/sda: 238.49 GiB, 256060514304 bytes, 500118192 sectors Disk model: SanDisk X400 2.5 Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: gpt Disk identifier: 8BF721E2-AA3C-43E8-A8B0-1B608E93C690 Device Start End Sectors Size Type /dev/sda1 2048 34815 32768 16M Microsoft reserved /dev/sda2 34816 346265599 346230784 165.1G Microsoft basic data /dev/sda3 346265600 347469823 1204224 588M Windows recovery environment /dev/sda4 437407744 496001023 58593280 28G Linux filesystem /dev/sda5 496001024 500117503 4116480 2G EFI System /dev/sda6 435453952 437407743 1953792 954M Linux swap Partition table entries are not in disk order. The first three partitions are related to Windows, including Windows Boot Manager. Grub is installed in sda5. I am using UEFI.