I have 2 HDDs in my Optiplex 755 and I was using the one with windows 7 installed. After that I wanted to switch to my HDD that has windows 10 by accessing the bios but I couldn't boot into it. Ive tried startup repair but that doesn't help and other things like resetting and keeping my personal files doesn't help cause I get an error. I don't have a recovery image and I was dumb not to make a system restore backup. Anything else I can do.