that happened to me when i tried to install 4.0.3 in uefi mode. i don't think it says 4.0.3 works with uefi. anyways, installing with legacy works.
however - it will break your system. probably. maybe you'll have better luck than i did. if you want to proceed,
mount the EPS file system.
save the /EFI/Boot folder, especially bootx64.efi.
sgdisk -b save_the_gpt /dev/xxxx
xxxx is your main disk
dd if=/dev/xxxx bs=512 count=1 | tee mbr-backup.raw | xxd > mbr-backup.hexdump
have a bootable linux usb or sd. qube os messes up the partition table and my bios no longer recognized the disk for uefi boots. none of the dual boot partitions on your hard drive will boot.
install qube os
reboot.
if you can't reboot into anything else, fix stuff as follows.
boot into the bootable linux
dd if=/dev/xxxx bs=512 count=1 | xxd > mbr.hexdump
edit it to change the 0x80 at offset 0x1be to 0x00
xxd -r < mbr.hexdump | dd of=/dev/xxxx bs=512 count=1
i don't think any regular partition tools will let you do that. they all see the gpt and let you edit that. you cannot go and fiddle with the legacy mbr. but if you could, all you'd have to do is make the first partition in the mbr unbootable (inactive).
once i flipped the bit from 1 to 0, my disk was recognized again.
i haven't figured out how to make qube os bootable after that. but i'm sure it's easier than figuring out which bit to flip.