To be honest, I don’t know, I had Windows, I just downloaded Ubuntu to a USB flash drive and booted from it, then I formatted the C drive and put Ubuntu there. before that, Windows worked fine, there were no modes, it just worked in normal mode.Welcome to the forums,
did you deactivate windows quick-start ?
did it run in live mode alright ? before you hit install.
did you download the correct version for your processor?
did you check the Sha sum before trying to make the installation,
you could try looking for both VMX [Virtual Machine Extensions] and SGX [intel safe guard] in your BIOS and enabling them,
you don't say what your kit is, it wouldn't be a Dell by any chance!