I tried to have win8.1 and ubuntu installed at the same time, anyway, I failed. My problem at the moment is that after that I had just Win8.1 or just Linux installed and my Laptop does not boot normally. I always Have to press F12 (Dell Latitude E6510 Laptop) to bring up my boot selection menu and select the boot method manually, so the same problem with Linux Legacy boot and Windows UEFI Boot. I tried every combination in the BIOS for the booting sequence I still get a blank screen if I don't select manually.
I hope this question is not a duplicate and that I have given you enough info.