Some threads that I have read suggest resetting the CMOS, but that is not an option for me right now. Everything on the computer is brand new with the exception of the GPU due to how hard it is to get one right now. I had a heck of a time trying to get the PC to post whenever I built it. After a week of pouring through forums and trying this or that, purchasing a super cheap GPU (GT 1030) allowed me to get into BIOS and change it from UEFI to CSM. That did the trick and allowed my older GPU to work. I returned that cheap GPU, so if I do a full BIOS/CMOS reset, I'm afraid that I'll be locked out of getting back in until I could use a different GPU to set it to CSM once again.